Hi @Vermeer Grange,
As @PinkElephant points out, check your account and the amount of devices you're allowed to use.
As for the login-issue, check my post of November 5th, 2021.
Personally I'm in the proces of switching to OneNote. Not perfect either (and no perfect way to export/import) but more options a.o. regarding hierarchy. And of course the fact that you don't have to revert to dinosaur-age versioins. 😉
Good luck!