Items are not stacking correctly

So, I'm pretty sure this might be due to a mod, but I've been trying to narrow it down and I haven't managed to get which one. So I thought I'd ask here for help in case. The specific issue is that items in my inventory wont stack properly.

For instance, if I punch a tree down to collect wood, the first block I collected goes to my hand. So when I punch the second block of wood to collect it, it drops, but instead of stacking with the piece of wood already in my hand, it goes to the second slot in my hotbar instead. Another example is that I'll get some dirt, and then when I'm placing it down later I'll accidentally place a block where I don't want it. When I harvest it again, it doesn't go back to the stack that it came from on my hotbar, where it should have gone, but rather into my inventory. That means that if my inventory is full, then the dirt wont be picked up even though there should be space available in the stack I'm holding.

The forge version I'm using is 34.1.25, for java 1.16.3. The modpack I'm using is "Fiefdom", albeit with some mods removed.

I'll leave the mods I'm using here, and I'd appreciate it if anybody can point me in the right direction in regards to figuring out how to fix this.



Edit: So, after some more testing, I forgot to mention that if I harvest something that should be stacking in on itself, if I leave my hand empty or use a tool, than the item still stacks as "normal". However, everything else I mentioned still happens with the items regardless. I've even tried to look at the metadata for everything in my inv use f3+h.