Hi Guishan,
thanks for your reply and I support you guys as best as I can. My details:
iPhone 12 Pro on iOS 15.6.1, iPad Pro 11'' from 2017 on iPad OS 15.6.1, MBP 16'' with M1 Pro on Mac OS 12.5.1 and Windows 10 Desktop on Windows 10 Pro 21H2 (19044.1889)
iOS 6.8.1 (633), iPad OS 6.8.1 (633), Mac OS 6.8.2 (1082) Mac App Store, Windows 6.8.2 (1084)
Yes
One vault with around 300 items across all categories, most of them are logins. No attachments stored. Cleaned up on Saturday, now at precisely 252 total items and on Sunday I had my last overwrite issue.