I was trying to buy items in bulk to give to the Recycle Beast, but there were some that, no matter how many times I tried to buy, I'd always get an error. I tried to refresh the page and the item was still there, I even opened in a different browser and nothing changed. I lost count of how many items were in this stuck state.

Edit: I just noticed that some items appear on my inventory even though they shouldn't be there anymore

I don't think so. But I didn't try to buy that many items at once again, so I'm not totally sure.