Sometimes it happens: one server does run for many months, no problems. Then you want to update one small item, and one gem needs to be updated... How long could that take?
The answer is: hours.
Not that I had to do much, it just was I had to do a long wait. A very long wait. A very very long wait. Because of a gem version mismatch, I had to update my Gem bundle, and because I could not get rid of the problem, I forced a Gem Update command to update all gems to their most recent versions. And that was what I better had not done... It took about two hours to update them all :(