I've been working on setting up some doors utilizing Create, I'm using the latest release of the Engimatica 6 modpack. When the doors are actually moving, they're fine. But as soon as they stop in either position, most of the blocks go invisible. There's still the buggy physics typical of blocks still being there, This includes the blocks I'm using for the door itself as well as part of the Radial Chassis.

Just came here looking for this exact issue. Made a tree farm using a windmill and saws with a chest on top. And a large number of them vanish from view and use (but still have the kinda bouncy "server thinks there's a block here" collisions. Placing a block where the old blocks used to be makes them re-appear and usable again (such as the chest to collect the output).

I'm having the same issue with a simple rotating harvester crop farm.
When I stop the contraption, most of the blocks simply disappear.
They will reappear if I right-click them with an empty hand.

Same modpack, Enigmatica 6.

sinfuldarkus provided a video of the bug in the E6 report: https://www.youtube.com/watch?v=4iEqtjOGDxk

Thanks for the report. Looking into the issue, this sadly cannot be addressed by create.
See EnigmaticaModpacks/Enigmatica6#2862 for details

Awesome, thanks!