Safari "Manage Website Data" appears broken in latest Catalina release (maybe earlier too?)

Trying to diagnose mysterious Safari behavior (see here "iCloud/Safari/Catalina - Cannot access Notes from Browser - WebGL error"). I thought I'd clear cache and remove all cookies and try again. Using Manage website data in preferences I tried deleting both individual and all entries. Immediately after clicking 'remove' or pressing 'delete' after select all, the entries go away for a few seconds and then immediately reappear. I have found a few mentions of this on the web, but no solution and no explanation as to what's going on. BTW: problem is same on 'broken' Safari and on 'clean' version on my test account.