Contacts List instability iOS v iCloud
I started fresh. Deleted contacts on iPhone, iPad and Mac. Only copy of contacts was on iCloud. Deleted all lists.
Then activated contacts on iPhone, iPad and Mac. (oddly the number of contacts on iCloud and Mac were the same and different than the number of contacts in the iOS devices)
Created lists only on iCloud. Added contacts to lists only on iCloud.
In a day or two, one of the contacts disappeared from a list in iCloud, but not on the Mac or iOS devices.
This is a recurring issue. I think Apple has bugs in iCloud and also has bugs in reconciling iCloud/MacOS and iOS.
MacBook Pro 13″, macOS 13.6