OK, I got it to work again, make sure the mythtv backend setup is closed, open a terminal window, run "mythbackend" and wait until you see that "Running housekeeping thread" is done and hit CTRL+C to close the backend again, then for some reason, loading the gui version of the backend setup works after this for me. (you might have to update libssl and openssl if you didn't already)
OK, I got it to work again, make sure the mythtv backend setup is closed, open a terminal window, run "mythbackend" and wait until you see that "Running housekeeping thread" is done and hit CTRL+C to close the backend again, then for some reason, loading the gui version of the backend setup works after this for me. (you might have to update libssl and openssl if you didn't already)