Problem Solved!
I had the
SC still connected via USB to the PC but Assistant 2 closed. I suppose I should have disconnected it but it was charging at low power and I forgot it was there!
However decided to have a look and see if there was an update notification on the
SC. There wasn't but there was a notification that USB debugging was running and that the
SC was set to use USB for charging. Previously there had been a notification that GO 4.3.36 was available and I had in fact successfully done that update via the
SC so that notification had gone.
I disabled USB debugging and that automatically disabled charging as both notifications disappeared..
I had a look in system settings to see if there was a sniff of a firmware update. There was but when I selected it a message to the effect that an update had failed because not logged in and to login to GO 4. Anyway logged in to my DJI account with email/password and the update was then allowed.
It downloaded to the
SC which had plenty of battery and space. This comes in a few parts. Download to
SC then setting up the update which takes a while and there was a pronged hiatus of many minutes at 16%. Then it hurried up and at 98% another extended wait. At that point it is checking the prepared firmware update is OK. When check is successful it reboots and then actually does the final install which is just a couple of minutes.
Update done! GO 4 opens with a warning that it is slow battery charging as the DJI standard power connection is not being used. Indeed it was actually connected to my laptop so
SC thought it was there for charging. So it looks like, but I forgot to check, that USB debugging and USB connection default is for charging and both seem enabled after the update.
So eventually update achieved when being logged on to my account seemed to be a factor. When it failed via Assistant I was in fact logged on there.
Hope this helps. Worth switching off USB debugging and being logged on to your DJI account if you have issues.
Unlike the January problems where I couldn't update via the
SC only via Assistant and that story is nearly a small book! Other way round this time.