I tried using the internal guider in place of PHD2 and ran into similar problems.  Everything ran very smoothly for a while, then guiding seems to have stopped.  It occurred to me that these problems are happening roughly 3 hours in to each session - I now suspect my laptop put itself to sleep, was then woken up by network traffic but didn't recover.  I'll do some more testing - this may well turn out to be user error. 

Thanks so much for your help!  

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