Contacts not syncing ONLY if entered on iPhone
If I enter a contact on any of my Macs or on iCloud.com, that contact then syncs to all devices perfectly, including my iPhone. Therefore, iCloud is working correctly on all devices. If I enter a contact on my iPhone, it ONLY is visible on my iPhone, and nowhere else - not on any Mac, not on Contacts on iCloud.com.
I've tried signing in/out, updating software, and confirmed that "Contacts" is selected to sync on all devices. This is a bizarre mystery, but very annoying. Thanks in advance!
iPhone 12 mini, iOS 15