Following on from :
I went out to do some testing last evening.
Step 1 - Turn on all sensors, precision landing, et al!
Step 2 - Remind myself what a manual landing is like with downward sensors on: Go up, come down — and THWACK!!!
Nothing damaged! 
Also, luckily, the “over water tests” were scheduled to happen later.
So - all sensors off/on/off etc. Power off/on/off etc.
- Absolutely no warnings that the VPS is faulty.
- Absolutely no awareness of the ground.
- Hover at head height - move hand beneath - no movement from the drone. (Ideal for hand catching, but that wasn’t the requirement here.)
Looking back through very old onboard DAT log files (I have an almost complete catalogue since Nov '16. OCD or what! 
), I managed to find one back when I still had sensors on, and the column “General:vpsHeight” had data.
Looked at the onboard DAT file from last evening … absolutely no data in that column whatsoever.
A strange one.
Anyone had this happen?
Anyone heard of this problem?
Anyone any ideas how I fix it?
(Remembering that I’m on really old V01.04.0100 firmware and similarly old/compatible Go4 app - for personal reasons. 
)