Do you have a long password? I had the same issue with a 64 character password. Apparently the web interface implicitly truncates long passwords to 60 characters, but Jerboa doesn't (Jerboa issue #425). Once I changed mine to a shorter password, it worked fine.
Yep, 66 characters. Tried changing it to a (much) shorter one, but still having the same issue. Reading in other communities, it seems that lots of people have problems with Jerbora, and lots of other people don't. (sigh).
Update: Seems that the password change didn't take. But deleting the last 6 characters of the password when logging into Jerbora seems to have worked.
Seems like there might be a similar issue with the old password length in Lemmy when changing the password. Ugh.