Maybe putting it on a riser with a quick release such as this guy ...
UTG LE Rated Double Rail/3 Slot Angle Mount with Integral QD Lever Lock System https://www.amazon.com/dp/B004RNC8RY/
... could help maintain the zero better if the Bushnell mount is not consistent and getting worn.
EDIT: whoops, saw you're using a riser. Perhaps the riser is the issue. The quick releases, such as in the above, seem more consistent in application of pressure when remounting.
UTG LE Rated Double Rail/3 Slot Angle Mount with Integral QD Lever Lock System https://www.amazon.com/dp/B004RNC8RY/
... could help maintain the zero better if the Bushnell mount is not consistent and getting worn.
EDIT: whoops, saw you're using a riser. Perhaps the riser is the issue. The quick releases, such as in the above, seem more consistent in application of pressure when remounting.