Same here. It started for me a couple weeks ago. It's a rather large pain. I thought about adding 2FA, but it doesn't help this problem at all, really, from what I can tell. Just makes it harder to get back in every other day.
I'd change my username, but it's stupid that Apple makes your AppleID be an actual email address, probably the easiest thing a hacker can find and use to try to break in. If I could just make up a unique username for my Apple ID, it would be that much harder for someone to get in.
That said, in my at-home experiment, I can verify that my wife has had not one glitch with her AppleID. Go figure.
I'm going to try shutting down some devices, and signing out of iCloud altogether on others just to rule out an errant login somewhere (though all of them have updated login info).
I'm sure it will magically resolve itself at some point. And we'll still not know why it's happening.