In my particular case, the peoblem turned out to be the socket converter I was using (in combination with a USB-to-USB-C cable).
Those white thingies with a USB opening that you plug into the mains.
Turns out some of them work fine for an iPhone, but if you plug in a FP3, the charging will be extremely slow, sometimes even de-charging.
We own two very similar ones. The slightly larger one works with FP3, the slightly smaller other one doesn’t. Go figure. Turns out I switched them.
