Nothing too exciting...
At Universal Hollywood in August, we queued for aaaages to go on the Mummy. We got on, sat down, restraints on... then it broke down. After a few minutes, they released the restraints manually, kicked us off and gave us a couple of priority passes.
On Oblivion on Good Friday, we'd just been loaded, then an almighty hail storm started just as the train was about to leave the station. They made us get off, wait outside the station until the hail stopped, then we got back on.
Also got stuck for a few minutes coming round the last corner into the platform on Stealth on Easter Sunday.
I wasn't on it, but I watched G-force valley, get evacuated and be reset on the Saturday over the Easter weekend. We were due to have been on the next run, so only just missed it.
I also remember getting stopped for about 10 mins on the lift hill of the Vampire when I was a kid. It started snowing, so me and my cousin had a competition to see who could catch the most snowflakes on their tongue. Helped pass the time at least.
I definitely agree with the comments about Thorpe being good for getting passes etc. We got exit passes for Inferno one day just for hanging around in the queue during a break down. We hadn't even been waiting that long. We also got park evac tickets one day last season, as there was a power failure which caused loads of the rides to close early.