Contacts won't allow addition of new contacts

I can click "+" to add a new contact. I then can add the name and the company, if any. I can add the first 8 characters of the phone number, but when I do the keypress to add the 9th character, it instantly closes that add-new-contact form and opens the next name on the alphabetical list (the one that would follow the new contact if it were completed), and it opens it in Edit mode.

I've closed and opened the app, itself, without benefit.

I've rebooted the iMac without benefit.

The HD part of the Fusion drive recently failed and was replaced, but the S.M.A.R.T. parameters of the new drive are perfect.

I find that I can add new contacts to Contacts on my iPhone and iPads, and I presume that they will flow over into Contacts on the iMac . . .

But what in the world is going on with the Contacts application? Might there be a way to uninstall it and reinstall it, even though it's baked into the OS?