Is the pellet sensor aimed correctly? It is supposed to be aiming at the auger hole. It is quite common for the pellets to hang up on the sides such that there are a lot of pellets in the hopper, yet the pellets directly above the auger are getting perilously low. The next time you get a low pellet error, take a photo of the hopper to show what is going on.
It is common for pellet dust to build up on the pellet sensor. Take a damp (not wet) towel and clean the actual sensor which is mount underneath sensor body. Perhaps that will help.
I used the pellet sensor when my Ironwood was new. Now I just fill up the hopper at the start of the cook and check the pellet level by eye every couple of hours. Generally, I will need to rake the pellets along the sides of the hopper into the center so they can feed into the auger. I refill the hopper as needed.
One thing you can try to help prevent the hangup of pellets on the sides is to spray the sides of the hopper with food grade silicone spray. For overnight cooks, some guys have rigged a hopper extension to enlarge the capacity of the hopper. This can be done with a bucket or suitable sized container above the original hopper with a hole over the auger.
