SOLVED:
You will need to scroll down and find the individual realms you remember had toons and log into them. Once your client sees that these (assuming updated for shadowlands and using new hardware) realms have your toons, it will move to the top of your list and you’ll see it correctly next time.
For those that CAN’T remember what realms you had toons on, unfortunately, you’ll need to log into EVERY. 
SINGLE. REALM. until you find them.