If a trident hits a block and the block is removed it can't damage things anymore but arrows can.
They also can't damage other things after hitting another entity but an arrow from a piercing crossbow can.
How to reproduce:
1) Put mobs in a 1 x 1 chamber
2) Place a block 2 blocks above the chamber
3) Through a trident at the center of the block
3.5) Put mobs in the chamber
4) Break the block and see the trident hit the mobs and none of them die.
How to Thing 2:
5) Put mobs in a 1 x 1 chamber with a open trap door above the first one
6) Through the trident at the mobs in the top chamber and then see it not damage the ones in the bottom chamber.
Linked issues
Comments 2
Thank you for your report!
We're tracking this issue in MC-130151, so this ticket is being resolved and linked as a duplicate.
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This appears to be a duplicate of MC-130151, which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.