Issue began with the DW asking me to remove the screen from the bathroom vent so she could clean the underside of the roof vent lid. We leave this vent cracked open for ventilation during storage (it has a vent cover on it) and it had become quite dusty/dirty. I thought it would be easier than removing the vent cover - but, when I removed the screen, the little tabs were so brittle they broke off. Decided to clean the other two vent screens and the plastic frames that hold the screens in place were very brittle on these as well. At one time, we used those foam vent pillows which, I believe, concentrated the heat and caused the plastic to become really brittle.
Found replacement frames with screens on Amazon for under $12 each. Simple fix. Four screws on each inside trim ring. Remove the knob from the vent bell crank. Replace the frame. Clean up all the sawdust and construction debris that fell out of the trim rings. Clean screens and a happy DW - life is good.