Welcome to PHD2. Ordinarily we need to look at your
PHD2 debug log to be able to say anything meaningful. I will hazard a guess that it could be related to your Settling settings in Neb. In Neb 3 there was a PHD Link option with settings for dither and settling, Neb 4 must have similar settings. If you set the settling tolerance too low or the time threshold too high, your mount may never be able to settle to that degree of precision for that long.