Periodically, while playing with Create, what can only be described as a "shadow" appears on various moving parts: windmill sails and linear chassis seem to be the biggest culprits. It will stay even after relogging. Only a restart of the game will help.

Minecraft version: 1.16.5
Java version: version 8 Update 291 (build 1.8.0_291-b10)
Windows 10: 19041.985
Forge version: Forge 36.1.17
Create mod version: 1.16.5_v0.3.1c

Here's why this is odd: I don't Optifine/Optiforge or shaders on, so having a shadow is baffling, to say the least. I made a video on YouTube showing this strange glitch: https://youtu.be/BonNxnxjLk0

This issue has been marked as stale because it has been inactive for 3 weeks. It will be closed if it remains inactive for another 3 weeks.

This issue has been closed since it has been inactive for 3 weeks since it was marked as stale.

What happens when you stop the contraption and start it again?

When it is stopped, the shadows disappear immediately. When I start them again, it varies: they'll either come back immediately or after a few seconds.

On the bottom right of the F3 screen it says "Rendered Portals: 1". Do the shadows still appear when it says "Rendered Portals: 0", i.e. when you don't have that nether portal in your view?

Hmmm, interesting. Would you mind posting a screenshot with the F3 menu open?

Sure. Not a problem.

Yes, it does:

The mystery deepens. I thought this was a separate bug, so I considered submitted another bug report. However, I've just discovered that they are related.

All of the entities that are showing the shadow effect I've shown here also appear in the Nether:

Suspecting it might be a strange interaction between Create and Immersive Portals, I've disabled Immersive Portals. It may be a coincidence, but it went away immediately.