When sorting an inventory (chest, or player) with at least one enchanted book in it the server immediate crashes.
This is a consistent issue that I've notice since upgrading to 1.16 and was not an issue in 1.15. I've attached 3 crash reports. The first two (order of timestamp) are from attempting to sort a chest of enchanted books and the third is trying to sort a player's inventory with only one enchanted book.
What you've done is absolutely amazing and I am so thankful for the work you've put in.

crash-2020-06-25_21.54.29-server.txt
crash-2020-06-24_20.37.23-server.txt
crash-2020-06-25_21.35.41-server.txt

I have found that you've fixed this in the 1.16 branch. Closing this and waiting for the update to be published.