GC clustering broken in 4.19 - causing crashes with MediaPlayer

There is a crash in 4.19 that’s quite bad:

LogObj: Warning: Object MediaPlayer /Game/Movies/MyVideoPlayer.MyVideoPlayer (0x000001fb95235780) from cluster Material /Game/Movies/VideoMat.VideoMat (0x000001fb957b7720 / 0x000001fba6ec6280) is referencing 0x000001fb8b0de4c0 MediaPlaylist /Engine/Transient.MediaPlaylist_11 which is not part of root set or cluster.

Error: Encountered object(s) breaking Disregard for GC assumption. Please check log for details.

I’m only seeing that crash rarely and it appears pretty random while a media player is running, and most often while unloading a level where there was a MediaPlayer playing before. I have heard about other people though where this crash happened more often.

The crash seems to be fixed by unticking this:


Is that a known issue? Is it fixed already in 4.20? I can’t really reproduce this, so that’s hard to know. If you also see this issue, please comment! I’m not sure how good of a “fix” disabling GC clustering is, since it sounds like that will negatively impact performance.

Yeah, had the same issue the other day on a released game. I couldn’t figure it out for the life of me, until finally I noticed the TV would cause me to crash with that error.

Very strange because we’ve been on 4.19.2 forever… and it’s just NOW starting to affect my game… So, we disabled GC Clustering and it resolved the issue. Obviously this comes at a performance cost sadly.

Does anyone from Epic has to say anything about this?

Have you filed a bug report? It’s the only way to get an actual response from Epic now - and be sure to provide a repro case.

I don’t have a repro case, so I have not filled a bug report. I only got that crash quite randomly. Victor Burgos seemed to have a repro case that always lead to a crash, but he’s probably too busy to create a repro project, especially when its so easy to just disable the GC clustering in the settings, which obviously isn’t ideal. So the only thing we can do is wait for someone at Epic who knows the GC stuff to see this thread.

I have the same issue. I can reproduce it in my current main project with 100% reliability by forcing garbage collection, but I struggle with reproducing it in a clean repro project.
Did your projects handle the playback via blueprint? For time reasons I used blueprints in the repro project (main project is code only) and I wonder if it could be related to this (I enabled “Blueprint clustering enabled” in the project settings, no change so far).

I’m getting this in 4.20.3 with the media player only when packaged. Anyone find a solution other than disabling clustering?

Thank you for this topic, I found that GC was cousing the problem with the media texture asset!

Hey all,

I did some digging and it looks like this is slated to be fixed in 4.21.

Thanks for letting us know!


Hello Tim,
I’m interested to know where do you found related to 4.21?
Do you have a bug number for this crash?

Thank you!

Would be nice if we could know more details about the bug so we can patch 20.3 ourselves…

Hey all,

I don’t believe the fix is listed externally as of this time, however, I will ask if it can be done.

There ya’ll go!