This bug was already reported in thread MC-144118. I am reporting this bug again because the previous thread was resolved, but the issue persists.

When traveling in the ocean, I stumbled upon a baby Drowned chicken jockey holding a trident. The chicken entity had a visible baby on its back, however the actual baby was invisible, chasing and throwing tridents from the ocean floor. Here is my best guess at the cause of the issue:

The jockey spawned on the ocean floor, where Drowned usually do.

I actually saw the chicken force the Drowned to rise to the surface, since chickens float in water.

This caused the Drowned entity to desync with the chicken.

While the baby was invisible, I was not able to hit them with a weapon, but I could still block the tridents with a shield.

Once the chicken was killed, the baby became visible and vulnerable again.

I think the fact that the baby had a trident was irrelevant to the problem, as thread MC-144118 reported the baby without a trident.

That is as much info as I could think of. If you need more information, I will respond to comments.