I have had some strange lasering events over a long period of time.  Results were inconsistent, or sometimes the laser wouldn't fire at all - or so I thought.  It was trying to fire and work properly!  Lots of times it did work properly, and at times I would blame it on the software.   I had the lens out for cleaning today and found a loose machine screw on top of the lens!  It appears to be a bed screw like those that hold the laser bed in place; at least it's the same size and thread.  I guess the screw was able to move around some at times and block the beam.  I have processed several projects with noticeably better results today.  The lens mount that holds the lens in place is magnetic and the screw was held to that, but obviously was able to move some.  The screw isn't damaged.   I do have the optional air assist with the nozzle that mates with the lens mount.  Let the comments begin!  I'm so happy now that I won't mind.