Playing through ATM6 pack (1.16.5) with no issues. Added in the mods in the title (although, think its ElectroDynamics causing it) and the pack crashes on opening load. Crash log (https://pastebin.com/DREdCSM1) refers to hellfire/astral sorcery and reliquary but I'm not sure the issue lies with these mods. Asked on Forge, was directed to ask Astral/Reliquary mod team as they are the ones referenced.

Any help in navigating would be much appreciated!

yes it's electrodynamics. was reported before in #544 and there's nothing I can do on my side.