Looking at your logs it looks like your GPS had a reboot in flight. There is a known issue where this happens occasionally with ublox GPS’s that I believe is getting patched in copter 4.0. If your copter was in Pos Hold I could see this being a reason it drifted off as it also appears that the copter has not been tuned. It wouldn’t hurt to check the connections going to the GPS to make sure they are secure. I’ve had the same GPS reboot issue happen to me three times on three different aircraft and I’ve never had a crash it would just go into the Land flight mode, so there could be something else at play here.
Many thanks for your reply. Yes tuning had not been done yet as the flight was to be just a hover test to ensure that everything worked well with the new LiHV battery. GPS connections are fine.