That's a very good point; the paper often has a tendency to come off the walls of the tube and to start floating around freely inside the tank, especially if smaller scraps of paper are used. If there's not much chemistry in the tank (which is typical when using drums), it's likely that the paper doesn't get processed evenly.You seem to be using quite small pieces of paper for your test prints and I doubt those can even be fitted properly let alone stay in proper position inside the drum with all the pouring in/out of chemicals and drum rotation that is happening
Another contributing problem can be if the drum is not properly light tight, e.g. because part of the light trap is missing. E.g. in Jobo paper drums, there's a cup attached to the cap that is an essential part of the light trap. If this is missing, light will enter the tank when the lid is removed for pouring chemistry in or out.