Whenever you light a nether portal or place slime/honey block the texture disappear and appear in the sky, this bug occurs in overworld/nether/end, but when a slime or honey block is placed on a piston/sticky piston the texture appears for half second,
and also the texture of the water glitches , between every falling water block a thin block (like a carpet) but have the color of water but darker,
these bugs occur in a flat world with redstone machines with slime/honey blocks,
and it can also happen when you update your 1.16.5 world to 1.17
(About The Photo):
The Nether Portal Is Actually Opened!
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Duplicate of MC-227859, which was later resolved as invalid due to this issue being caused by optifine. Disable this modification in order to resolve the problem.

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This report is invalid, as your game is modified while experiencing the issue.
Please only report bugs that can be reproduced in a vanilla (unmodified) environment.
OptiFine is considered a mod in all circumstances.