well turns out to be simple, and actually not new - if you have the outer margin set high [upwards of 16000 pix, it seems to vary] then the guides mis-behave;

was the same up to a point in ver 15.1 - I just happened to set up a default template in pro+ with a high outer margin value, don't think I ever noticed it before, or maybe forgot... like you do... I think...