Hello, I am using the Fantasy MC Fabric modpack, which includes Souslike-Weaponry.
I've started battling the bosses, but the Fallen Icon keeps crashing my game.
I thought it might be the java version, but it is 17.0.8, and I couldn't figure out how to change it in CurseForge.
There was one occasion where the game didn't crash on the first spawn, but it did on the 2nd spawn.
In CurseForge I have it set to use 8G of RAM, and I've tested my RAM for being faulty, and it seems to be good.

In the end I made a server, and started it and joined via localhost, I was then able to fight the boss with no issues (but for some reason my inventory isn't synced and that's a separate issue). The server starts with JRE 17.0.10+11-LTS-240, so potentially that might be the problem?

Attached below is the crash log.
hs_err_pid30124.log

Also, once I join back my save, after a crash, my game is rolled back a few seconds before the crash (I still have my essence of eventide and am in my original spot) and the Old Moon Altar is gone.

Also, it doesn't happen with the Returning Knight, Just the Fallen Icon.

i have the same problem, for me it helped to deinstall sodium, but only once lol
but i play in singleplayer

Same here, first time i summoned him it crashed just before he did a big attack. Then second time it crashed just as i spawned him.

I don't know why, but I can't replicate the issue, so it's hard for me to know if I've managed to fix it or not, but at least I tried. Will make an update shortly, make a new issue post then if the issue persists.