Assertion Error When Upgrading to UE 5.6 – Sequencer Related Crash

Hello,

While trying to upgrade my project from 5.3.2 to 5.6, all blueprints related to Sequencer cause a crash during project startup with the following error:

“Assertion failed: !Object->HasAnyFlags(RF_NeedLoad | RF_NeedInitialization) [File: D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\Serialization\AsyncLoading2.cpp] [Line: 10517]”

I can upgrade the project to 5.5 without any issues, but this problem occurs only in 5.6.
Maybe it’s a bug—I’m not sure.
Does anyone have any ideas?

Hello there @Galasdaer!

Considering that 5.6 has just released, it is still prone to unexpected issues. Since the problem only occurs with that version, I would test with migrating your project contents to a clean, 5.6 project. As well, please perform a cache refresh, via deleting Saved, Intermediate, and DerivedDataCache folders.

Hello @brs-sebascova !

You’re very welcome, and thank you for your reply! Yes, I’m aware that the engine is still quite new, but it’s frustrating that I was able to upgrade to 5.5.4 without issues, yet I can’t do the same with 5.6. As you suggested, I tried with a clean cache and even attempted merging into a fresh 5.6 project—but no luck. I’m still getting the exact same error.

From what I can tell, the blueprints causing the crash are somehow related to Sequencer. What’s even stranger is that I still get the error even if I completely clear out the blueprint’s content—unless I delete the blueprint entirely.

If I remove the pre-defined maps from the config and let the engine load into an empty level, I can open the project. However, I can’t even rename the problematic blueprints—let alone open them. As soon as I try, the same error appears again and causes a crash.

I really hope this gets fixed with a hotfix :frowning: