Blueprint doesn't work after upgrading to newer version

Hello.

While working in UE4.20, I created a Blueprint (parent class: StaticMeshActor) for a building block that lets me easily mix and match different types of windows and doors on the same base mesh.

It worked fine until I upgraded the project to 4.21. Now I get the error message:
[Blueprint name] contains invalid data.
Data validation FAILED. Files Checked: 1, Passed: 0, Failed: 1, Skipped: 0, Unable to validate: 0

This happens even when I made a new Blueprint in the current project to try and narrow down the problem.
None of the nodes are highlighted with a red Error sign so I have no idea what is causing the problem.
Thanks in advance.

edit: in Compiler Results, I get the error Default__[BlueprintName]_C is not valid. See the MapCheck log messages for details.

edit2: false alarm. The problem disappeared when I restarted the engine.

I meet this problem,is there any method can fix it

Same here. Is this a bug reported to EPIC or anyone figured out how to solve it? Thanks