I have added ReplayMod so I can take cinematic videos of my builds in a server. For some reason, whenever I open my inventory, I crash. I've removed Replaymod from the mods folder and it doesn't crash, but if I readd it it crashes again. I'm suspecting it's a mod conflict or something with the version of forge I'm in., since I'm playing on a modpack, but I can't understand crash logs.

Crash log: https://pastebin.com/Mp5AD80H

Hm, unfortunately the crash report did not contain enough information for me to figure out the cause nor the mod which it's conflicting with.
Could you try narrowing down the conflict by throwing out half the mods at a time until you're just left with ReplayMod and the conflicting mod?

I'll try that out soon.