EragonTheEldest

Figured the issue out. The server didn't have a copy of the "feathers" mod, which I think was the issue. Thank you so much for the reply, though.

For any of the players on the server, hovering your cursor over any armor item (in an inventory or crafting grid) in the pack immediately crashes the game, with the following crash report: https://pastebin.com/NGjFwCiH If you hover over the items in JEI though, it just says "Tooltip Error, See Logs", and does not display the item name, though you can still see the recipe. On singleplayer though, it works fine, both in JEI, and actual items in chests and such.