The bug
When a mob is killed by lightning attracted to a lightning rod from a channeling trident it doesn't count as a player kill, not dropping xp or higher loot rates.
How to reproduce
Make a chamber like this (the trident has channeling on it):
[media]Spawn mobs in the chamber
Press the button twice and see the mobs be killed but no xp be dropped
I can confirm that this occurs in 21w11a. I briefly thought this might be MC-206922, but I was able to confirm that the experience orbs are not dropped at all by setting up a repeating command block with the following command.
When a mob is killed by a channeling trident directly, "Experience orbs were dropped." is printed in the chat (and the experience orbs are destroyed by the lightning). However, when a mob is killed by lightning from a channeling trident hitting a lightning rod, nothing is printed in the chat.
This is not unique to lightning rods. If you summon an invulnerable armor stand and throw a channeling trident at it, any nearby mobs that were killed by the lightning will not drop experience orbs.
This behavior might be intended, though, because the player is only killing the mobs indirectly.