Newbie - Not always picking up items

I am new so please be patient. Initially when I was wandering I would pick up all items. Now at higher/lower level in Dungeon suddenly I can see objects but I am not picking them up despite having room in bag.

Do you run with hireling? If yes, full hireling inventory will prevent picking up items for your main too even if you still have room for them.

please always check if your inventory is full or pick up at option menu