Altitude degradation in forward flight

Hardware: Pixhawk APMCopter 3.1.2 Vulcan frame Hexa
Problem: I mainly fly mapping grids at 50 - 70m. Problem started recently. Aircraft oscillates wildly in altitude. Worse in wind. Tried test flight in no wind. Aircraft rapidly loses altitude then rectifies. Vibrations acceptable until the end of the run, then goes wild. After setting down it still tries to fly. Props eat dirt.
I attach two logs. One aborted mapping flight and test flight.
Up to now everything has been working great. How do I get my hexa back to the happy stable dependable again?

Perhaps I need to ask more specific questions with Yes/No answers for maybe getting support?
Plot: AccZ; BarAlt; Alt; DAlt; Spd
Does the Barometer look healthy?
Are the errors caused only by the AccZ vibrations?
The vibrations only happen in forward flight and are more bias to the negative (not equal positive and negative from -10) Does this mean that something is touching the pixhawk only in forward flight? If that were the case would I not see AccX and AccZ vibrations as well?