So, I recently encountered one heck of a bug. It's taken me days to figure it out, so I'm hoping somebody could make use of this information.
One day, out of nowhere, putting a specific book on a bookshelf crashed all clients in range of the player and (bibliocraft) bookshelf in question, and thereafter corrupting the chunk. During investigation, I also noted that using a shell storage from the Sync mod, specifically, initiating any clone transfer, caused the same crash. The two crashes are interchangeable, and are thusly:
internal exception: io.netty.handler.codec.DecoderException: net.minecraft.util.ReportedException: Loading NBT data
internal exception: io.netty.handler.codec.DecoderException: java.io.IOException: packet was larger than i expected, found "numbers and packet here"
After going through a ridiculous amount of threads, to which no consensus could be reached, I started doing things the hard way. The answer turned out to be a particular book from one of the lostbooks' book packs, one of the HP Lovecraft ones. The Case of Charles Dexter Ward, to be specific. If any player has had that book in their inventory, it corrupts their player file. I tested this every which way and backwards. I've since destroyed all lovecraft books and moved them out of the lostbooks directory, and deleted old player files, and now everything behaves normally, even with the old inventories, sans-books.
Shame, too. He's my favorite author.