Not sure without actually seeing the set up but if it was exactly the same configuration that can only leave the focusing, perhaps it was way out of focus! The moons of Jupiter should be (almost) pinpoints of light whilst Jupiter would show a smallish disc (as you described) . I cant think what else it would be. The Moon will be back in the evening sky next week and you could check your focus technique on that ie craters are sharp, then check for point like stars and Jupiter as described. I would not think that your mirror is lose and cause the focus to shift.
On your second point I would suggest that the scope did not equalise with the outside temperture. I have my scope permently set up outside in a a shed with a roll off roof (luxury ) and even that suffers from the temerture difference when the roof is drawn back to observe. Those pieces of glass do hold the heat and take time to cool. Try and give it 30 minutes at least before expecting to much and take into account what we said earlier about tube currents and seeing conditions.