You log in, confirm it with another device (better hope it’s nearby! That first setup of a 2nd client is a doozy of a feel bad, if it isn’t),
Your devices don’t have to be nearby to verify them. You can enter a key backup passphrase instead.
then a few days later it just stops letting you do anything,
That’s not normal. Looks like you ran into a bug. Did you report it, so it can be tracked and fixed?
I gather from their weekly reports that they’ve been fixing encryption bugs lately, and that the clients now in testing (the Element X code base) seem to have them solved. You might want to try those, or one of the third-party clients.