ARSP without a speed sensor

I am flying fixed wing plane with pixracer and the newest software.
No Air speed sensor. While I am experienced flying with airspeed sensor, I have difficulty this time without it.
Can somebody more clever have a look at the log and try to identify where the problem is.
My speed limits are set to 11-22 but the ground speed sometimes drops as low as 3.
Wind up to 6m/s. The plane barely flies against it even though the THR was set to 80 in auto modes.
Link to the log