Flight-mode error and EKF/InertialNav Check/variance on 3DR Solo with 9 GPS-sats

After a few sec in air Tower warned about gps glitch and Solo went to Alt-Hold. Tried to get back to Loiter (as logs show at 3 min), Logs show Err_subsys 10 code 5 => failed to change mode to loiter).

After this Err subsys 16 Ecode 2 and then Ecode 0 => (meaning: EKF/InertialNav Check ECode 2: Bad Variance ECode 0: Bad Variance cleared)

There was 8/9 GPS-sats all the time, and I can’t find any reason for the Solo to go into Alt-Hold and then ECode2 bad variance. (Except if the GPS constellation was really really bad that hour).

Any suggestions on the log analysis?