From looking at your graph, I think the problem is with your HVAC. The dips are more frequent during the heat of the day, not so many during the nighttime hours. Re-read this old forum post (posted above) of other users with the same problem.
You may need to replace your Run/Start capacitor or add an additional Hard Start kit. I installed a brand new HVAC system and had this problem. I think my power cables to my HVAC are undersized based on the distance from the meter panel to the outside compressor. They meet NEC code, but they are not large enough for the power demand on ‘starting watts’.