Minecraft - 1.16.5
Forge - 36.1.16 (in a modpack) and 36.1.23 (Latest at the moment of writing this issue.)
Applied Energistics 2 - 8.3.0 (in a modpack) and 8.3.1 (latest at the moment of writing, releases, not alpha or beta builds)
AE2WTLib - 0.0a-1.16.5 (Latest at the moment of writing)

Used default Forge installer to setup a server. To reproduce: put AE2WTLib and AE2 into mods folder on Forge server and get this crash related to AE2WTLib's mixins. Removing AE2WTLib from the mods folder solves this problem. If you need more info: feel free to ask here.

Crash without everything: https://gist.github.com/DenisMasterHerobrine/e481ec7c9faa1acc99d986a5184843b3
Crash in a modpack: https://gist.github.com/DenisMasterHerobrine/9a1c5f2342cddd53899ed3627f5f5f31