I hooked up a reverse osmosis water filtration system to my refrigerator. The water still comes out the door (a bit less pressure), but the ice maker has stopped producing ice. I rechecked the lines on the back of the unit and everything looks fine. Suggestions?

The fact you hooked up the water filter, there's your culprit. Most water filters do not flow at the same rate as the water would have before the filter was added. Nothing you can do about it except enjoy cleaner water.