Thanks for your helpful suggestions.
I haven't tried Fast charging the car using the MyEnergi app.
As I understand it, Fast mode imports electricity from the grid if the PV panels are not generating sufficient power; but my aim here is to trickle charge from PV alone when there is sufficient surplus, and avoid any use of the grid.
Also, the problem is not with getting the Zappi to start charging or getting the car to accept the charge.
I can start to charge the car from the PV panels in "Eco+" mode, it's just that it keeps terminating the charging process prematurely every time the surplus electricity falls below a threshold, instead of waiting until surplus becomes available again then re-starting to trickle charge automatically, as it had done up to a couple of weeks ago....
Re: Zappi firmware, I've just checked using the information here:
...and it turns out that there is a new version of firmware for the Zappi available.
There's also a new version of the MyEnergi iPhone app available.
I'm not sure whether these updates have come out since my system was working fine; and I don't think this would explain why the MG firmware keeps resetting the Scheduled Charging to "On" after it has been repeatedly saved as "Off".
However, it's important to exclude out-of-date Zappi firmware or MyEnergi app as potential causes for my charging problem, so many thanks for thinking of this.
I've downloaded and installed the latest versions of the Zappi firmware and the MyEnergi iPhone apps and I'll see if these make a difference.
Thanks again for your helpful suggestions.
Best wishes