Guiding depends on many variables and repeatability from night to night is not trivial. We all blame the software at some stage but in my experience it's been always seeing conditions or mechanical issues on the night, would it be balance, stiction, temperature drop with worm/gear meshing, power fluctutation, how tired the operator is, the list goes on. Some night it will be perfect, the next nothing will work for no apparent reason. Just get used to it.
