I bought 5 of these little catfish about a month ago. I tend to always see 3 of them active, day or night. The other two hide most of the time. I once used a flashnight at night, and I saw all 5 of them grazing the glass.
So your cats are probably hiding behind a fixture. You will know if any die because your water quality will go way down.
These fish are timid, so do not think they are dead. Use a flashlight at night, you may just find them grazing your glass or live plants at night.