Assertion Error When Upgrading to UE 5.6 – Sequencer Related Crash

Development Programming & Scripting
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1

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?

1 Like
2

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.

3

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:

5

I have the same issue,but not Sequencer , an animBP.5.5 is fine,5.6 crash.
[2025.06.12-09.22.48:035][713]LogWindows: Error: appError called: Assertion failed: !Object->HasAnyFlags(RF_NeedLoad | RF_NeedInitialization) [File:D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\Serialization\AsyncLoading2.cpp] [Line: 10517]
Object=‘ABP_—C /Game/—/ABP—.Default__ABP_—_C’ (000001A62F9FC000), Flags=Public | ClassDefaultObject | ArchetypeObject | NeedLoad | WasLoaded, InternalFlags=0x04504000

6

This is a pure blueprint project,I don’t know if this matters :sob:.

1 Like
7

Yeah i think we need to wait hotfix or something :frowning:

2 Likes
8

Same issue here on exit of UE5.6, I kinda figured,ty for verify everyone.

1 Like
9

Hope it will be fixed in 5.6.1, i can not open that bp file,crash immediately

1 Like
10

Yeah, still waiting for hotfix.

11

Same issue , Please Epic Fix this … It crashes a lot of BPs and Widgets …

12

Still waiting…

13

completely same QAQ

14

We have the same issues on multiple assets after switching to 5.6

The only temporary workaround is to do

			if(Object->HasAnyFlags(RF_NeedLoad) && Object->HasAnyFlags(RF_WasLoaded))
			{
				Object->ClearFlags(RF_NeedLoad);
			}

before the failed check code ( We are also hitting the same check in UObject::ConditionalPostLoad() )

It could potentially lead to other issues, but at least you could open the editor until the proper fix is made

15

5.6.1 still has that problem,i have to delete the problem file to let it work

16

Yeah, still same crash, exact same error. Maybe we should submit bug report

17

I’ve debugged this issue for the past couple of weeks.

In our case it was caused by this CVar linker.EnableFullBlueprintPreloading being set to False in our project. We had to set it to false when we migrated to 5.4 due to a bug related to cyclic dependencies, but it seems they’ve fixed the 5.6 issue but broken something else in 5.6 which was also causing silent data loss in recursive Instanced classes, so now you need to turn this back on.

It should be under DefaultEngine.ini

[ConsoleVariables]

linker.EnableFullBlueprintPreloading=True

Or just remove it if it’s false because the default is true