I must say that I did see some strange behaviour with stock Jarvis 16.1 and the stock opensubtitles.org plugin 5.0.16. I searched for a title, was not the one I was looking for and then tried to check a second time. This time the subtitle search stalled. Trying again, I received a message that there was an error with my login (even though the credentials are correct and I my first subtitle search and fetch were successful).
I'll try to post a debug log next time.