Cartridge filter issue

I have a four cartridge filter pentair system. Haven’t had any issues until about a month ago. The filters keep popping off the seat inside the housing. These are aftermarket filters but I’ve had them for about a year and a half with no issue till now. I catch it when I notice that filtration is minimal and pressure drops. I can go back and open up the housing and put the filters back in place but only last a few days then the same thing happens. Any clue why this would start happing all of the sudden?