If your polar alignment is poor , particularly in Dec , your PHD2 graph will display typically what your experiencing ( Dec pulses with graph below central line ) Also whilst imaging for an hour or two another tell tail sign is significant Declination drift in one direction left of right. Your object or target can drift a long way left or right after an hour or two
Try to get you PA error below 10 arc minutes or even better down to a few arc minutes.Between 1 and 3 arc minutes is more than adequate for PHD2 to work its magic. As Bruce and Andy have mentioned many times on the PHD2 forum , don’t be obsessive or paranoid about sub arc minute polar alignment, it won’t make you guide any tighter.
Below is a handy PHD2 tutorial on typical guiding scenarios and actions to remedy most issues
https://openphdguiding.org/Analyzing...Guide_Logs.pdf
Hope you resolve this minor issue with your guiding ( your guiding generally looks pretty good )
Thankfully your not experiencing huge spikes in Dec or Ra which is more difficult to pin point
Good Luck
Martin