MRpack server loading failing on use with extra files in mod folder

[xavoriancapitalprovince-bot]

Please confirm the following.

• I checked the existing issues for duplicate problems
• I have tried resolving the issue using the support portal
• I have ensured my Modrinth App installation is up to date

What version of the Modrinth App are you using?

Modrinth App 0.17.5 windows 10.0.26200

What operating systems are you seeing the problem on?

Windows

Describe the bug

Modrinth Pack is Failing on load when uploading files in the mod folder that are a part of the mod, the mod that is causing the issue is MCEF due to files in the mod folder to open in Minechromatic mod. the Files are causing a compatibility error due to not being added to the modpack

Failed to save server compatibility ModrinthServerError: [invalid_input] Error while validating input: Field version_number failed validation with error: regex

when adding the files manually into the modpack, the files fail to load on the client side

Steps to reproduce

1. install MCEF , Minechromatic and ultreon devices mod
2. open pack and stop instance
3. export modpack
4. Upload modpack to modrinth server service

Or

Download WeBuildHK modpack, this is suffering from this issue

Expected behavior

the modpack to update normally and to unpack the files without any errors, other updates have worked normally

Additional context

Install report: WeBuildHK
Result: failed while resolving pack (filesystem_error)
Job ID: 3b21c450-5918-409a-8db6-6442052063cf
Request: install_pack_to_existing_instance
Status: failed
Current phase: rolling back

Environment
App version: 0.17.5
OS: Windows 11 Home
OS kind: windows
OS family: windows
Architecture: x86_64
Kernel: 26200

Timeline

1. 2026-08-11T11:50:32.299946500+00:00 Queued install_pack_to_existing_instance install
2. 2026-08-11T11:50:32.305767+00:00 Started install job
3. 2026-08-11T11:51:12.042737300+00:00 Started downloading pack file for WeBuildHK project=k2vjndmE version=5cgYuUwN
4. 2026-08-11T11:51:51.485386500+00:00 Started resolving pack for WeBuildHK project=k2vjndmE version=5cgYuUwN
5. 2026-08-11T11:51:51.487871300+00:00 Started reading pack manifest for WeBuildHK project=k2vjndmE version=5cgYuUwN
6. 2026-08-11T11:51:51.490486100+00:00 Started resolving pack for WeBuildHK project=k2vjndmE version=5cgYuUwN
7. 2026-08-11T11:51:51.654317500+00:00 Failed while resolving pack (filesystem_error): I/O (std) error: unexpected BufError
8. 2026-08-11T11:51:51.654317700+00:00 Started rollback (restore existing instance legacy:WeBuildHK (3))
9. 2026-08-11T11:51:51.655642800+00:00 Rollback completed

Failure
Code: filesystem_error
Phase: resolving pack
Message: I/O (std) error: unexpected BufError
Operation: read modpack manifest
Source path: downloaded mrpack bytes
Archive entry: modrinth.index.json
Project ID: k2vjndmE
Version ID: 5cgYuUwN

Raw snapshot
{
"job_id": "3b21c450-5918-409a-8db6-6442052063cf",
"instance_id": "legacy:WeBuildHK (3)",
"kind": "install_pack_to_existing_instance",
"status": "failed",
"target": {
"type": "existing_instance",
"instance_id": "legacy:WeBuildHK (3)"
},
"phase": "rolling_back",
"progress": null,
"details": {
"type": "empty"
},
"display": {
"title": "WeBuildHK",
"icon": "C:\Users\61423\AppData\Roaming\ModrinthApp\caches\icons\3e2ad4d8b221ac40d2af4e6da521051affdbb770.png"
},
"error": {
"code": "filesystem_error",
"phase": "resolving_pack",
"message": "I/O (std) error: unexpected BufError",
"context": {
"operation": "read modpack manifest",
"source_path": "downloaded mrpack bytes",
"entry_path": "modrinth.index.json",
"project_id": "k2vjndmE",
"version_id": "5cgYuUwN"
}
},
"rollback_error": null,
"created": "2026-08-11T11:50:32Z",
"modified": "2026-08-11T11:51:51Z",
"finished": "2026-08-11T11:51:51Z"
}

Latest launcher log excerpt
File: C:\Users\61423\AppData\Roaming\ModrinthApp\launcher_logs\session_20260811_173956.log
2026-08-11T17:39:56.846737+10:00 INFO theseus_gui: Initialized tracing subscriber. Loading Modrinth App!
2026-08-11T17:39:56.850053100+10:00 INFO theseus_gui: Initializing app...
2026-08-11T17:39:57.764796300+10:00 ERROR get_loader_tags: theseus::state: Attempted to get state before it is initialized - this should never happen!
2026-08-11T17:39:57.764796400+10:00 ERROR get_game_version_tags: theseus::state: Attempted to get state before it is initialized - this should never happen!
2026-08-11T17:39:57.765080400+10:00 INFO initialize_state: theseus_gui: Initializing app event state...
2026-08-11T17:39:57.765658700+10:00 INFO initialize_state: theseus_gui: Initializing app state...
2026-08-11T17:39:57.765676200+10:00 INFO initialize_state:initialize_state{app_identifier="ModrinthApp"}: theseus::state: Connecting to app database
2026-08-11T17:39:57.800986900+10:00 INFO initialize_state:initialize_state{app_identifier="ModrinthApp"}: theseus::state: Fetching app settings
2026-08-11T17:39:57.801172500+10:00 INFO initialize_state:initialize_state{app_identifier="ModrinthApp"}: theseus::state: Initializing directories
2026-08-11T17:39:57.801682300+10:00 INFO initialize_state:initialize_state{app_identifier="ModrinthApp"}: theseus::state: Initializing file watcher
2026-08-11T17:39:57.801805800+10:00 INFO init_watcher: theseus::state::instances::watcher: Initing watcher
2026-08-11T17:39:57.948211400+10:00 INFO theseus_gui::api::utils: opening command None
2026-08-11T17:40:19.177198900+10:00 INFO authenticate_finish_flow{code="{MODRINTH_ACCESS_TOKEN}"}:connect: theseus::state::friends: Connected to friends socket
2026-08-11T17:40:35.447522800+10:00 INFO create_shared_instance_invite_link{instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" max_age_seconds=None max_uses=Some(10)}: theseus::api::instance::shared::publish: Creating shared instance before first invite instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" user_count=0
2026-08-11T17:40:36.167053100+10:00 INFO create_shared_instance_invite_link{instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" max_age_seconds=None max_uses=Some(10)}: theseus::api::instance::shared::publish: Created remote shared instance instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" shared_instance_id=ACLu7wmo
2026-08-11T17:40:36.169731700+10:00 INFO create_shared_instance_invite_link{instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" max_age_seconds=None max_uses=Some(10)}: theseus::api::instance::shared::publish: Publishing shared instance content instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" shared_instance_id=ACLu7wmo
2026-08-11T17:41:09.355869+10:00 WARN create_shared_instance_invite_link{instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" max_age_seconds=None max_uses=Some(10)}: theseus::api::instance::shared::publish: Failed to publish shared instance content instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" shared_instance_id=ACLu7wmo error=Shared instances API request failed: error sending request
2026-08-11T17:41:09.356042700+10:00 ERROR theseus_gui::error: error=Shared instances API request failed: error sending request span_trace= 0: theseus::api::instance::shared::invites::create_shared_instance_invite_link
with instance_id="local:451fa026-70e2-43c6-b0a8-7424eb52b307" max_age_seconds=None max_uses=Some(10)
at packages\app-lib\src\api\instance\shared\invites.rs:60
2026-08-11T18:01:21.688552800+10:00 ERROR theseus::state::friends: Error handling message from websocket server: Protocol(ResetWithoutClosingHandshake)
2026-08-11T18:01:23.764415500+10:00 INFO connect: theseus::state::friends: Connected to friends socket
2026-08-11T18:01:46.982810300+10:00 WARN theseus::event::emit: Instance webuildhk has crashed! Visit the logs page to see a crash report.
2026-08-11T18:02:44.600273900+10:00 ERROR theseus::util::rpc: Failed to run RPC server: I/O (std) error: An existing connection was forcibly closed by the remote host. (os error 10054)
2026-08-11T18:07:01.537988500+10:00 INFO theseus::api::jre: Expected Java version 17, and found 17 at C:\Users\61423\AppData\Roaming\ModrinthApp\meta\java_versions\zulu17.64.17-ca-jre17.0.18-win_x64\bin\javaw.exe
2026-08-11T18:07:01.573722700+10:00 INFO theseus::api::jre: Expected Java version 25, and found 25 at C:\Users\61423\AppData\Roaming\ModrinthApp\meta\java_versions\zulu25.32.21-ca-jre25.0.2-win_x64\bin\javaw.exe
2026-08-11T18:07:01.574107+10:00 INFO theseus::api::jre: Expected Java version 21, and found 21 at C:\Program Files\Java\jdk-21\bin\javaw.exe
2026-08-11T18:07:01.656634300+10:00 INFO theseus::api::jre: Expected Java version 8, and found 8 at C:\Users\61423\AppData\Roaming\ModrinthApp\meta\java_versions\zulu8.92.0.21-ca-jre8.0.482-win_x64\bin\javaw.exe
2026-08-11T21:18:36.841448+10:00 ERROR theseus::util::rpc: Failed to run RPC server: I/O (std) error: An existing connection was forcibly closed by the remote host. (os error 10054)
2026-08-11T21:34:10.834643100+10:00 ERROR theseus::install::runner: Install job 65381f1e-4fae-4b3a-8894-5fffac0032de failed: I/O (std) error: unexpected BufError
2026-08-11T21:36:06.851816500+10:00 INFO theseus::api::jre: Expected Java version 17, and found 17 at C:\Users\61423\AppData\Roaming\ModrinthApp\meta\java_versions\zulu17.64.17-ca-jre17.0.18-win_x64\bin\javaw.exe
2026-08-11T21:39:37.925222700+10:00 ERROR theseus::install::runner: Install job d3b324f4-a7b2-4766-b4ef-cf83732c0b0b failed: I/O (std) error: unexpected BufError
2026-08-11T21:51:51.654155700+10:00 ERROR theseus::install::runner: Install job 3b21c450-5918-409a-8db6-6442052063cf failed: I/O (std) error: unexpected BufError

[xavoriancapitalprovince-bot]

I managed to fix the issue on the webuildhk pack after removing the config settings, then adding manually to the mods folder