Modrinth App 0.19.1 fails to install CastCrafter Survival Server with unexpected BufError

[roeschfelix-stack]

Please confirm the following.

• I checked the existing issues for duplicate problems
• I have tried resolving the issue using the support portal

Is this an issue in the control panel or with the Minecraft server itself?

Control panel (on Modrinth.com)

What browsers are you seeing the problem on? (if a panel issue)

No response

Describe the bug

Bug description

Modrinth App 0.19.1 fails when attempting to install the "CastCrafter Survival Server" modpack.

The download appears to complete, but the installation fails while reading the modpack manifest:

filesystem_error: I/O (std) error: unexpected BufError

Error context:

• Operation: read modpack manifest
• Archive entry: modrinth.index.json
• Project ID: 5PJnGfrC
• Version ID: E8TbcgEl

The same error occurred twice consecutively.

Environment

• Modrinth App: 0.19.1
• OS: Windows 11 Pro
• Architecture: x86_64
• OS build/kernel: 26200

Expected behavior

The modpack should download and create a new instance successfully.

Actual behavior

The app fails while resolving the downloaded .mrpack file and then rolls back the partially-created instance.

Error

filesystem_error
I/O (std) error: unexpected BufError

Operation: read modpack manifest
Archive entry: modrinth.index.json

Job ID:
edc5040c-0fb6-4d30-98cb-e49ac664535e

Steps to reproduce

1. Open Modrinth App 0.19.1 on Windows 11.
2. Find "CastCrafter Survival Server".
3. Start installing/creating an instance from the pack.
4. Wait for the pack to download.
5. The installation fails while reading modrinth.index.json.
6. The app rolls back the instance.

Expected behavior

No response

Additional context

C:\Users\roesc\AppData\Roaming\ModrinthApp\launcher_logs\session_20260828_124617.log