While generating new chunks in end this crash error keeps happening.

The game crashed whilst feature placement
Error: java.lang.IllegalArgumentException: "byg:features/mushrooms/imparius/imparius_mushroom_canopy6" is not a valid tree part.

You can prevent these biomes from generating by removing the line
{
"data": "byg:imparius_grove",
"weight": 3
},
in the file end-biomes located at C:\Users\Admin\curseforge\minecraft\Instances\All the Mods 8 - ATM8\config\byg\

I think it works fine now with the update 1.0.21.

I second this, using 10.0.20 on multimc and was getting crashes because of those darn mushrooms. deleted the line suggested by Cyumm in the config and the crashes ceased.

Same issue and same error on version 1.0.20

Sorry forgot to mention, this crash has been occurring on 1.0.20. It seems like it’s almost a guaranteed crash when using a jet pack and loading a good number of chunks rapidly. I never encountered the crash on past versions due to never being in the end so it may have been an issue before this version.