This phenomenon happens to me on occasion also.  My setup: ap900, maximDL6, lodestar, guiding thru ASCOM (happens with relays also).  There does not seem to be a rhyme or reason to when it happens, but it does show tendencies.  My movement is always in RA only, happens in about 20 minute batches, and might ruin a sub or two or three in succession.  I am running in an observatory unattended and all night (weather permitting) so loosing a couple of subs in a session has never been a big deal. I just chalk it up to "$#!@ happens".  I might see it once or twice over the course of a month.

It happened the other night, so here is a drop box link to the track.log file and a jpg crop showing the effect on a 20 minute narrowband (OIII) sub.  It jumped 3 times during this sub at 1:12:03, 1:18:29 and 1:21:35.  As usual, the rest of the night was without incident.

link:

RA_guiding_issue

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John D