After restart UE, Static mesh lightmap is totally different, why is that?

Model is imported by datasmith from vred. UE4.21

After import, it is perfect. as in P1

then I save and restart the program, the lightmap seems completely destroyed everywhere. as in P2

Same model, same file. Just a reopen , I did nothing else. Why is that?

This might help you?

No, I did not do any re- import.

same file, close UE4, and re open. comes this problem.

Are you sure it’s not like a streaming pool over x error, but you’ve just turned off the error messages?

no error messages has been seen

Hello,

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https://epicsupport.force.com/unrealengine/s/

Thanks