Use tweezers to hold the rolling paper.

Press the key lightly on the paper and pull outward.

Try this at eight different angles from the center of the key.

If the felt pad is making proper contact, you should feel a drag. If you feel that there is little or no drag, then you have identified the key that needs to be repaired.

Hopefully, there is only one side of the key that has this issue. Otherwise, you may need a new felt pad.