Using Leather Works version 1.71.2 for MC 1.12.2, and Forge 8.0.99.99.

I'm having issues using packs in multiplayer.

They work just fine in single player, but trying to move anything in your inventory with a pack's GUI open while on a dedicated server prevents you from picking up any items in your inventory at all, and if you instead shift-click items into the pack's GUI, they don't actually go in, and instead causes some desync in your inventory when you close the pack. As in, you can click the slot where the item was in your inventory even though it appears empty, and the item will still be there, and doing so will properly update the contents of your inventory visually.

As for other stuff:

1. I'm wondering if it's possible to add other mod animal hide/leather or knife items to a list of items that may function with this mod? I did try adding them to toolKnife and resourceHide with CraftTweaker, but I guess that doesn't actually do anything in regards to the mod's function(I was kind of hoping I could give more uses to a variant of knives in this pack; while I could certainly script this in manually, I was wondering if it is possible to do without). I'd really like to integrate most if not all leather processing in my pack to be through this mod; while I've disabled their default recipes, now some items are just not quite as useful.

2. Would it be possible to add JEI integration on how to use the mod's mechanics? At the very least, description pages detailing how to use different blocks/obtain different items would be pretty helpful for players who don't want to keep the page on Curseforge open to see how to use the mod.

3. Not sure what you can do about it, but I can't find a way to prevent the ground trap from Pam's Harvestcraft from generating ready-made leather, and it'd be unfortunate to disable the entire thing because there are some food ingredient items you can only obtain through it.

4. EDIT: Remembered another thing! Crafting leather strips(leather + shears) doesn't seem to consume the leather in the process. It may also be a server specific issue but I haven't tested it on just the client yet.

i wish you would have broken these up or posted a comment on the page. I can't close only part of an issue...
0) That's going to be a tough one. I don't know when I'll get to it, but it's now on the list

1. Yes! The update I'm working on now, I changed the crafting to be better with Jei and the Ore Dictionary, Specifically for Primitive Tools knives. Those are indeed the correct id's.

2. Overhauling the recipes fixed most of these issues. Exceptions are in-world crafting and flint scraping. It is possible to add JEI support for those, though it is low on the list for me

3. No. She hard- codes all the drops here: https://github.com/MatrexsVigil/harvestcraft/blob/master/src/main/java/com/pam/harvestcraft/tileentities/TileEntityGroundTrap.java#L226 Nothing I can do to touch it. I suggest asking her to use loot tables

4. Works fine as far as I can tell. Submit another issue if you continue to have it.

Apologies. I wasn't sure if I should split it up or not since on other issue trackers sometimes don't have a problem with people putting multiple things into a single issue, but I can see that perhaps here the individual things were too different from one another to really warrant that.

Good to hear most of the stuff has already been looked at/worked on, though, and for #3 I did leave a suggestion on her issue tracker about it, so thank you for the heads up.

As far as #4 goes, I just went out of my way to test it on just the client to see if it works there, and in single player it is indeed functional; the issue was happening on a dedicated server specifically, though, and considering the first issue I mentioned here was also server-specific, perhaps it needs to be tested more thoroughly in that kind of environment?

Gotcha. I'll test the last one on a server.