Am just wondering if any conclusions can be drawn from this:
Three corners are solid, but not the one in the centre of the plate.
The bed was levelled before printing (and checked afterwards also). Even though the photo may appear to show a slant or lower corner (where the print is coming off), there is not. The bed is level, relative to the extruder, at room temperature.
The temperature of the bed is about 70 °C. I get inconsistent readings (with laser thermometer) but to the finger it feels about the same everywhere.
It's a glass bed, presumably with some coating. Is it degraded? Local temperature variation? Any ideas anyone?