Comaanion App says "inactive character"

I have been trying to login on the companion app today, and every time I do, I have to select the character to be displayed, I select my main character, and then confirm it, at which point the app comes back with a message "Inactive Character" "Your linked character in no longer active in-game. Returning to the home screen."

Error Code: 311003

It was working just fine yesterday. I have not done anything to change the status of that character (Dsherman Siren on Hyperion) I am even logged into that character from a Windows PC right now. There is no problem doing that.

I have logged in to that character and logged out again more than once using the game client on Windows PC. The app even briefly shows my character on the confirm screen, including an equipment change I did earlier today. (The problem had occurred both before and after that equipment change,)

So what has gone wrong with the app?

(No, I have not updated the OS on the phone. It is an Android OS on the phone, but the OS has not been upgraded to Android 10.)

Whatever went wrong, it seems to have been corrected. The problem did continue to occur every time I tried for 2 days. But this morning, it worked correctly.

I still have no idea what I might have done to cause the problem.

I also have no idea what I might have done to fix it.

But for now, it seems to be working again.