I actually had 2 clown loaches jump out to their death but that was in the span of the last 10 years. Both cases were when they were recently enough put in a tank. The first one was shortly after I moved the clowns to the pond, providing they had spend their time in another open top glass tank with no jumping but I think they needed time to settle in the new surrounding and that particular loach was super friendly and hyper active. Very sad. I had had him for a good few years. The second time was a newly purchased, again very hyper active baby clown loach, the reason I had picked him in the shop, he jumped out of his quarantine tank, also open top. I was devastated.
Apart from that, zilch jumping of fish in open top tanks. I have 2 open top tanks with hillstream loaches and a tub with a weather loach, open top, another with kuhli loaches, also open top, etc...No one ever jumps out. So in my opinion, they only jump out when stressed, either water conditions, stress from being moved, tank mates, etc....I'd be worried if I start getting jumping fish on a regular basis.