Minecraft Version: 1.10.2
Inventory Tweaks Version: 1.61-58
I'm not sure if I should leave this here or in the Refraction issue tracker, so feel free to correct me.

I recently experienced a client-only crash on a server when I selected a refraction mirror in my hotbar.
https://pastebin.com/F7aMk951

Actually, this might be a problem on Refraction's end.

Figured it out - the server didn't have Refraction added, but the client did.