I Also had alot of issues with many features of it, it couldn't connect most of the times. Now it works but again I can't remove an old lost phone. I don't think it's the right thing to do to release an app which is not stable or has a button which doesn't work...
The losers didn't think about adding a way to remove old phones. Don't use it or you will get stuck with a record in file explorer which will show all the files from the phone. It will take gigabytes of space, you won't be able to view any file.
Ok, you can disable the old device like shown...