In early teenage years I went with friends to a summerland, a park type that is mostly play structures, motor based circuits swimming pools but also a few carnival type rides.
I went on a double swinging ride, that is doing a full rotation type. I went on that ride, and midway the shoulder bar went loose and I had it like hmm.. 50 cm open. I was alone in my row (row of 2 seats, and not easily seen because of walls) I braced against the front wall the whole ride. I wasn't happy camper. But because I was alone plus being deaf, early teenager embarrassed etc, I did not tell them, I just went off and walked from there.
Park: Skara Sommarland, ride: dubbelkorven
At Liseberg, simulator movie with moving seats. Simulatour.
The strap went off and I was strapless. I jumped off it. Did not report here either.
Then other than those "could have gone wrong" things, I have only gotten badly treated and such, but it is less of personal danger and more of "I feel mistreated" ways so I won't list.
Oh yes, I forgot, at Lisebergsbanan, Liseberg, one quite recently the train got held up at the section brake/booster combo thingy and had to wait a few minutes, and then we got released and went on the whole circuit. Nothing odd in Planet coaster in poorly designed coasters
But IRL it wasn't too fun. If not in know of how coasters work one could easily get nervous being slammed into, but it is not so. (but instead opposite, precisely because of that.)