Critical Navigation Failure during takeoff with 2 GNSS Antennas (HERE3)

During takeoff, my VTOL Duo Tailsitter encountered a critical navigation failure and I had to recover it manually in atti-mode. I am using two HERE3 GNSS antennas, one located in the nose of the aircraft (orientation = NONE), the other is located on the back of the wing (orientation = PITCH+90). This arrangement worked reliably for probably more than 100 flights so far in MR and FW mode!

During the flight today, both GNSS antennas showed a permanent 3d-fix, more than 15 satellites and no GPS jamming and noise during the entire flight. But the watchdogs for position, vertical velocity and airspeed got activated as can be seen in the logfile.

Any ideas?

Here is the logdata:

https://review.px4.io/plot_app?log=9b2fbd46-b14b-4130-b248-9b3a4923178a