minecraft 1.12.2
mine colonies 0.8.5875

Not sure how to duplicate this. I had been using the clipboard for about 20 mins, and one time I right click on it to see who needed the bow I was bringing and it crashed.
crash-2017-12-05_19.58.09-client.txt

Fixed in the upcoming version (should only need a few minutes)

I just experienced this issue on a LAN server, mod version 0.8.8026. We're using a modpack called World of Dragons if that matters at all.
Here's the crash log:
https://pastebin.com/czhDWxhx