nah, definitely not too many mods. I've ran far more than this before without issue. And again, have ran a server with a very similar modpack for 1.5 years without issue
I found the problem was that I was editing MY playerdata, when I actually needed to edit the WORLD'S playerdata, since the hosts' inventory is apparently actually documented in a separate spot. Everythings' working fine now, though.
After doing this, the items delete from my inventory, but after I load up my world, it crashes again. I check the editor afterwards, and the items have found their way back into my inventory, despite them having been removed before loading the world again. How do I get them to stop coming back?