Also remove impactful from the server
client-side-only mods are mods making "player" related changes which a server does not have
HUD mods, Minimaps, Mods adding/changing settings, graphic, animation and sound mods etc
Then the level.dat is broken
Create a new world with the same settings
Then copy the level.dat, level.dat_old and session.lock from the new world to the broken one
Delete the new world and test the broken one - if this is working, upload this world to the server
There are client side only mods in your server files
Remove giacomos_hud, oculus, iris, enhanced_boss_bars and epicfight
You can keep these mods in your client
Maybe also remove essentials