GoSund Smart Plug not flashing (3 of 4 devices)

I got some Gosund Smart Plugs from Ama**n recently, and managed to flash only one of them without opening.

However, as opposed to other people here, this is what I get in

==> scripts/smarthack-psk.log <==
^CTraceback (most recent call last):
File "./psk-frontend.py", line 113, in
main()
File "./psk-frontend.py", line 106, in main
r,_,_ = select.select(readables, [], [])
KeyboardInterrupt

Obviously I am not doing any Keyboard interrupts .. this seems to come from the Timeout.

The board of the device I opened was showing version 2.4 - I managed to flash this through serial, but would of course be nicer to do it over the air.
Any experience how to get this done ?

Start with scripts/smarthack-psk.log and psk-frontend.py, especially the select.select call reported in the traceback. Reproduce the timeout with the affected Gosund plugs and compare it with the device that flashed successfully. Done means identifying whether the version 2.4 devices can be flashed over the air and documenting or correcting the failure path.

Written by the indexing model from the issue text.