Sometimes when reentering the app it puts my account between signeditn and signed out. Meaning, that I can still upvote posts and see my comments/posts but loose acces to the subscribed tab.
I've experienced this once as well, though I didn't gain any insights into why it happened or what could be done to prevent it. I worked around it by logging out and back in again.
This has now happened to me like 3-4 times in the last 24h. Not sure if there's something off about how the instance my account is on is managed (it's quite new), but this is happening to me a lot... and it doesn't self-recover as the other commenter experienced.
If you go to App info for Jerboa and tap Force stop to kill Jerboa's process, then when it restarts it will log in successfully again. This is a lot nicer than signing out and retyping a strong password. Still not sure what causes it, it happens to me every few hours. But killing Jerboa and letting it relog in is a useful workaround.