When the Neon Engine is placed in the world, it is invisible and other rendering issues happen such as the player's right hand and the item they hold mirroring to the left side of the player view. It doesn't happen 100% of the time but I couldn't figure out what makes it do this. If the engine is off-camera, the other rendering issues disappear.

Noticed a somewhat similar problem that happened to me a few times while testing the pipes, tank & pump. Not sure what caused it exactly but the player model became invisible, and so did the fluid inside the tanks. It seems that quitting the game and starting a new world make the problem go away, only restarting the game does.

Actually all entites disappear (mobs, tile entities, etc)

Having tested things more, it seems the first rendering issue with the engine depends on the orientation of the engine block. When the player is facing north the engine can be placed without issue, but when facing other directions it causes the bug.

Still not sure what causes the second rendering issue exactly, except that it happens whenever doing stuff with pumps+pipes+tanks