I noticed that you can put chests inside chests, and then NBT copy those into more chests. Long story short, I created a chest item so dense it kicks me when I join. Is there a way to reset just my inventory? or should I restore from a backup?
You can use /clear command. or use the restore backup
To reset the inventories do the following:
Download your world, remove the playerdata or players folder in the world directory and upload the map again.