Not critical but tiring bug (I think bug or better omission). After renaming blueprint with a thumbnail (created before by Asset Actions/Capture Thumbnail) thumbnail is cleared. Clearing is not necessary, because this is same blueprint (in this case actor bp), with same object etc, just name changed. With a lot of actor blueprints for rename what is sometimes required, this is no good.
Thank you.
Edit - topic changed, thumbnail gone when asset is moved to different directory.
I have reproduced this issue and logged a report for it here
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Still an issue in 5.2.1. The link to the issue shows “Wont Fix”. Now either Epic are bunch of @#$!?/'s, or it is a version reason. It better be the latter.
As of UE5.3 you can fix your thumbnails by resaving assets with broken thumbnails. For example, you select assets with broken thumbnails, right click one of them → Asset Actions/Load, then after assets are loaded, you again right click selected assets and click Save. After save is done, your thumbnails will be fixed. Probably works same way on other versions too.