Looks like my Hoymiles 800W microinveter has died on the 11th Nov and I only now just noticed.
Either that, or the Deye generator input is doing something strange.
Tried power cycling the thing and nothing. Don't really want to go on the roof right now and remove the panels, might have to wait until next year.
I do have a 4 input version of the Hoymiles I can swap in to test if needed.