[mcguyver]

It could be a very simple fix. Open the gun up and remove the upper receiver, it will make it easier to work on.

Drive out the bolt stop latch pin, keeping care to not lose it or the spring underneath. Then, with some small needle-nosed pliers, pull up on the main board up front until the red sensors are exposed. Wipe them off with a Q-Tip or similar if they have any grease on them. Then put it all back together.

You can clean the sensor holes on the sector gear with a sewing needle to remove grease if it's there.

What you describe can also occur if you have removed the sector gear and re-installed it backwards (resulting in the sensors not be able to read it properly).