Summary:
When zooming in with a spyglass, the trident can be seen flashing lines.
This is not a problem with the spyglass, as a close inspection of the trident sometimes shows flashing dots. They were simply invisible without a spyglass.
Each trident has these lines, in which the "owner" of the trident is alive.
The lines indicate roughly the host of the trident. It is also easy to reproduce with drowned ones.

Steps to reproduce (1):

1. Throw the trident into the ground.
2. Move 5 blocks away from the trident (approximately).
3. Look at the side of the trident through the spyglass.

Steps to reproduce (2):

1. Write the command: 

   /effect @s regeneration 1000000 255 true

2. Spawn a drowned man with a trident.
3. Go into survival mode.
4. Have the drowned man shoot the tridents and lure him about 5 blocks away from the trident.
5. You can go to creative mode and look at the trident (don't kill the drowned man! Mandatory!)

Observed results:
Incomprehensible stripes will be visible at the tip of the trident.

Expected results:
The trident should not have flashing and rotating lines in a circle.

Image:

Video:
Minecraft 2021-08-19 23-01-01.mp4
Minecraft 2021-08-29 10-41-36.mp4