MacOS Contacts disappear while entering!

There are thousands of users who have been experiencing this problem through at least the last 4 versions of macOS, and it persists. I've seen no permanent fixes, although several workarounds have been suggested. Why Apple has failed to resolve this problem programmatically over the last many years is a mystery and a black eye for the macOS team there

For me wiping my iMac (because of a hardware problem) and reinstalling the OS from scratch, which requires installing all programs from scratch, solved the problem, but that's drastic and extremely time-consuming.

The workaround that seems to be easiest is to scroll to the very bottom of your list of contacts. There you will find a bunch of similarly named entries that are blank. The Contacts app places one there every time it screws up your attempt to add a new contact. If you open one of those, you can edit it, fill it in completely, save it, and it will persist. It's basically the same process you did before the bug bit you but with the addition of a few mouse clicks.