I spent a few minutes recording on a friend's server only to find out that the recording gets stuck in an infinite loading loop. the world doesn't even load, it just says "joining world" for a few seconds before saying "loading terrain" for like one frame.

in singleplayer the mod works absolutely fine with no problems, but when I view a multiplayer recording everything breaks and I get softlocked.

using hypixel as an example of what I see

Please reproduce the issue and then attach the latest.log file.

here's the log file
latest.log

Could you try to remove all other mods and see if it loads then? If it does, please try to re-add them to identify which mod may be causing the issue (there's nothing obvious in the log).
I'd recommend starting with Immersive Portals cause that's know to malfunction in replays (though idk if that would still apply with hypixel replays, since hypixel doesn't have IP installed).

So by disabling every mod installed (apart from iris, sodium, and all that since the version of RM I use requires it) and trying to play the replay, I got the same result. So I recorded a new replay with all mods off (with iris, etc still on) and it worked fine. Enabled mods one by one with no issues. Even with every single mod enabled and playing the new replay, there were no issues.

So something goes wrong during recording rather than playback.

decided to just use a separate installation in my multimc for recording in servers and only use mods i know that work/actually want like fps displays and zooming