Tropical fish don't appear to be able to pathfind around stairs placed underwater; if they move into a stair block (regardless of whether or not it's waterlogged) the fish will spin around in place endlessly.
Can't really depict the problem in a screenshot, so I've attached a video file
Have a nive day Mojang!
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I have experienced this before on an infinite world and it's not only stairs but they can get stuck on most blocks.
GoldenHelmet
MCPE-58605, MCPE-60210 and MCPE-60497 are either new duplicate reports or else reporting an amplification of this bug in 1.14/1.14.1. I believe it is the latter because I have seen drowned spinning and briefly getting stuck when trying to swim since 1.14 too.