Entities sometimes don't render behind the water surface on Fast or Fancy graphics

Please take a screenshot with your F3 screen enabled.

ok

Check Fabulous graphic and you are using any resourcepacks?

No, at that time I did not have the faboulus grafic activated, and I do not have any texture pack.

Thanks to MC-202132, we now know this is caused by low entity render distance.

From MC-203657

Interestingly it only happens to the
 most recently spawned type of entity. If I spawn a bunch of turtles 
they will all be affected. However if I place an armor stand the turtles
 will cease to be affected, but the armor stand will until I 
place/summon a different entity. If I spawn a squid and then a turtle 
and then two more squid only the last two squid are affected. Very 
strange.

50% render does not appear to be the cause.

Affects 20w45a
Reloading fixes problem until new entities are spawned.
Increasing Entity Render Distance does not fix the problem.
It only happens on fast and fancy graphics.

I cannot reproduce in 20w45a

To make this slightly clearer (a summation/clarification of the above):

• This behaviour happens in groups. E.g.: In water, place three minecarts, then an armour stand, then place two more minecarts. At certain angles the first three minecarts are affected, at other angles the armour stand is affected, at yet other angles the last two minecarts are affected. Not necessarily the same angles.

• This can also occur for fully submerged entities (does not have to be partially submerged initially).

• This happens vice-versa; if the player is submerged in the water, entites in the air can also be invisible.

• Fast/fancy graphics only.

For me entity distance does not seem to be a factor.

I can still reproduce in 21w06a

Also affects above water

While they are underwater , enabling hitboxes (F3 + B) shows them and the hitbox

this still occurs in 1.16.5

No, their hitboxes become invisible as well.

Intended, this also happens in real life so not a bug. 

@Trplob WAI needs a proper Mojang source, not just "this also happens in real life". I addition, this ticket already has a Mojang Priority, which means Mojang consider it valid.

Affects 21w11a

@Trplob Water refractions and the bending of light in real life is very different from improper translucency and layering in a video game.

I agree with Trplob, this is not a bug. I often see turtles in real life that I cannot fully see it through the water surface. Works as intended, please resolve.

it seems to be a drivers issue you seem to be playing on a laptop with intel HD graphics which are known for giving a lot of errors and crashes on different games

This still occurs in 1.16.5

I still don't know how to fix the bug and it is getting really annoying, I've had time where I'm doing stuff in water and a drowned zombie appears out of nowhere and it's terrifying

You can play on Fabulous! graphics to fix the bug.

Can confirm in 21w17a.

I can confirm that this also affects 21w18a.

Seems much worse in 21w18a.