The bumblebee catfish has a couple of small spots that could be colouration or something else.
1 spot is on the dark patch just under the dorsal fin, where it meets the body.
Several spots on the pectoral fin.
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Assuming the water is good (0 ammonia, 0 nitrite, nitrates less than 20ppm, pH around 7.0), and there are no chemicals in the water that are causing the irritation, I would say there is a low grade protozoan infection in the tank. It could be whitespot, velvet, Trichodina, Costia, Chilodonella or something else.
You could try heat treatment where you increase the water temperature to 30C and keep it at 30C for 2 weeks. That should kill all the different types of protozoans in the water. Clean the tank and filter before raising the temperature, and increase aeration/ surface turbulence to maximise the oxygen levels in the water.
Or you could try medication again, but I would try heat first because it doesn't involve chemicals.