Editor crashes trying to launch a session for projects with migrated MPCs

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Assets

Summary

We are having an issue where some projects that have Material Parameter Collections, which were migrated from other projects in a previous version of UEFN, seem to cause crashes on load. If one of these projects is opened, no other project with MPCs can be opened without crashing until we delete all Unreal folders under ~user/Appdata/local/. The odd thing is, this doesn’t happen on every project, just a few specific ones. We’ve tried Fixing Up Redirectors and Resaving all assets, but the problem persists.

Steps to Reproduce

Open a project that has MPCs migrated in a previous version of UEFN. Open a new project that has the same MPCs.

Expected Result

Editor to open without a crash.

Observed Result

Editor crashes on open.

Platform(s)

Windows

Additional Notes

Appologize for this being so vague in terms of repro. The issues have been a bit inconsistent across projects, but there are 2 particular ones that are causing issues for us. We’d be happy to provide Epic with the repo to take a look at the specific MPCs causing issues.

Update: its seems like something with the MPCs is getting cached in this folder:

AppData\Local\UnrealEngine\Common\DerivedDataCache

This is the only folder I need to delete when switching between projects to avoid crashed.

It seems some elements are being cached / shared across UEFN projects. It appears its looking for MPCs in previously opened projects.

3 Likes

The status of UCB-1344 incident has been moved from ‘Awaiting Validation’ to ‘Closed’. Resolution Reason: ‘Duplicate’

Just wanted to say thanks for the bug report, your solution made it possible to continue with our work.
Appreciate it!

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