Did you upgrade from NX 11.0.0?
And do you have this issue for more Parts/assemblies, or just this one?
Just to check, are you sure the update was correct? NX was not running during the update?
Please consider reporting this issue to GTAC, we have a couple of similar issues already being investigated so it would be good to know if yours is a new one, or a duplicate. If your issue is closed against an existing PR you will be notified when it is fixed. Based on the reported cases, these issues do not occur in NX11.0.0 mp4.