Victron 12/12 30 Orion Tr Smart Isolated not charging…

Help!
I have an isolated 12/12 30 isolated setup in a camper trailer.
It is plugged into a BT/50 Mazda (DMax).
It seemed to work when I installed it months ago.
Now, it will only continue to cycle through, “Charging Disabled” and then briefly “Charging Disabled Due To Remote Isolation Inactive” (or the phrase for “you have me switched off at the plug thingy”).
Plug is in - continuity checked.
Makes no difference to try a correct wire to either polarity of the plug input/output.
It will deliver power in “power supply” mode.
It is colder now than when installed (Australian cold, more than 10°c!).Cable run is overall maybe 8m. No huge voltage drop…
I have turned off the engine shutdown sensing and the cutout function, to rule them out.
Latest software.
Thoughts? Voltage drop under load??
Cheers?
David