Hi Max,
Have you tried guiding with PhD2 as if the behaviour is replicated it suggests a mount issue although unlikely.
I have not had a problem since changing to one pulse dithering and keeping aggression down in RA.
I have noticed recently that star detection generally (in focusing, solving and guiding) is significantly adversely affected by binning. I have never noticed this before. I tried 2X binning with the ASI120mm and a pop up said that this was not supported. I am pretty sure that this has not been the case previously.
Luckily removing binning in solving and focusing modules has restored normal star detection behaviour.