Hello !
Let's contextualize first:
So I was messing around with the new snapshots and I decided to do a cage of tinted glass. When I put a Strider in it, I decided to put torches around the cage and at while going around the Strider suddenly disappeared ! I wasn't looking straight at the Strider but when I did it reappeared. My FOV is set at 100 and there is no particular settings I have.
By what I have tried out this bug has some conditions:

• It only happen if you don't look directly at the entity but some angles won't "hide" the Strider
• If you're in a "bug angle" and you do f3+B (show hitboxes) the entity will show no matter what
• If there is some parts of the entity that are outside of the cage, they will show but darkly (as if they were in the tinted cage)
• It only happen if you didn't pause (for a certain time, and apparently will still work but for some extreme angles?) or restart your world
• Doesn't work with the Wither / items
• Works with non-moving entity (e.g. armor stand) 

I sent you every screenshots I made to make it clear, but I think it'll be easy to reproduce this bug haha.

Have a great day !