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