Large tricopter QuadPlane Project, tuning problems

Hi everybody,
We are working on a Y3 tricopter QuadPlane, where the rear motor has a yaw servo and a tilt mechanism combined. The size of the plane is about 1.8 m nose to tail and 4 m wingspan with MTOW of around 25 kg.
We were able to fly it alright without the wings attached but now with the wings we are having issues with oscillations in roll and yaw directions. The plane is sometimes able to hover without oscillations for a while but any disturbance will cause it to slowly oscillate, sometimes uncontrollably. We have been trying to tune the relevant PIDs but results have not been good. The tricopter tailwag came back after adding the wings, we were able to tune it out quite well before.
A possible problem I can see is the flex of the aluminum profile that is used to mount the two front motors. We will stiffen it up soon.
Increasing the roll P radically has made it a bit more stable but it is hard to tell which is the worse problem as the tail wag happens at the same time as the roll oscillation. Any tips and help would be appreciated!

Logs for a test flight with mostly Qhover and Qstabilize, attached to a pole to prevent damage.

Logs for the most recent test flight with mostly Qloiter tests.

I will post pictures and maybe test flight videos later.