I had a problem concerning Snapmarks and then discovered that I was not getting the red beam which checks for material height. Support even emailed me that I would have to return my Glowforge for repair or replacement. I read a comment on the forum from a user urging another user to make sure the windows on either side of the lens were clean.
I have read every word of the Glowforge cleaning instructions. These two windows are not mentioned and there is no instruction to wipe them off. I have cleaned my lens many times, but never the windows. Below are before and after photos of my print head. I now get a clear red beam as I shoud.
Perhaps the cleaning instructions should include these two windows.