The curling I am experiencing is not on overhangs, it is on a flat portion of the build, printed without a raft or a support. And it is not especially thin, perhaps 6 mm.
On turn-on the printer says The Creator Firmware Version 1.0. I have never tried to reload the firmware, this is as delivered. The preheat function has never worked differently that it does now and it seems to be the same for the extruders as for the bed.