Well, pastebin didn't like how long it was. Good news, I have Google Drive, so I jury-rigged it and pasted the log there. (It's 400 and change pages, sorry.)
EDIT: I ought to mention that I've tried to enter my world multiple times, and I've restarted client a couple times as well, so I've no idea what's going on. I'll pop into my world for a few seconds before it loads (I can see my waypoints and my hotbar has stuff in it), but I'll be kicked before the world can load in. I tried losing focus before I spawned in, and the game didn't kick me until I unpaused. That's all I've got in terms of helpful info, I believe.
Hmm...did you try putting, say, a bag of holding into a backpack, or any bag of items into another bag of items, by chance?