Had one several years ago and sold it. I had problems with it sinking down in use. I think you might not be pushing the router up far enough, and that you may have it so low that you're hitting the end of travel block. If not, and after reading the instruction sheet, consider returning it to Rockler. I used mine with a Bosch 1617 and occasionally had a little trouble inserting the router motor into the lift's jaws. It would bind until I wiggled it and it would come loose so I could push the motor up.
With the lift lowered as far as possible, you want to insert the motor so the bit is just below the plate's surface. That will give you a full range of adjustment. I occasionally cleaned up the inside of the lift where the motor fit. Don't lubricate it!
As much as I liked the idea of the setup, I later switched to a Triton TRA001, which has a built in lift, plus some good safety interlocks. The router didn't cost much more than the Rockler lift. I kept my oldd 1617s for freehand use, so each base has its own motor. Nice.
The more I do, the less I accomplish.