In the latest snapshot the game crashes if a BlockEntityRenderer is registered in any way and you activate a piston via redstone. The block that uses the BER does not need to be placed in the world, or even be capable of rendering anything. If it simply exists and is registered, the game will crash when activating a piston.

I'm not entirely sure why this happens, but I can confirm that it has happened for both me and NinjaPhenix on the latest snapshot when we each registered two entirely different BERs.

Here's the crash report: https://hastebin.com/yacixegaxe.http

On the first sight this looks like a classloading issue, as both mod might have caused the block entity render dispatcher to load too early.

Where crash report is from

My previous analysis:

if npe, it is vertexConsumerProvider blockState this.manager or this.manager.getModelRenderer()

Apparently in 9c45b1e (19w39a update) the lazy block entity renderer registration scheme is removed. This may have been the cause of this crash.

Mechanism is explained in #430

a1ff8ff