Resolved,
It has been a long night
but I finally found it.
Strange...very strange but the sonoff units I have with the USB BUB II set-up is unable to be flashed with the standard tool provided by espeasy (esptool.exe flash.cmd). Instead I used the
https://github.com/nodemcu/nodemcu-flasher nodemcu flasher software.
However, and this for those having the same problem, I needed to push the button UNTIL THE FLASHING has started. So way over the 10 sec. after the power-up. Not sure why, perhaps one of the real experts
can answer this.
I tried several times with the standard tool but in my setup and with my 10 units I was unable to flash them with the standard tool.
I expect some timing errors as I saw that the esptool flasher was sending and receiving some bytes but stopped waiting for an answer of the sonoff...until time out.
So for those having the same problems
1 Download nodemcu-flasher
2 Select ESPEasy_Rxxx_1024.bin file
3 Hold down the switch of the sonoff unit...
4 Power-up unit...
5 Still hold the switch down...
6 Start nodemcu flasher...
7 If RX TX lights from USB BUB II FDTI unit are flashing you can release the switch...However if the flashing stops (I had such a unit) you need to push the switch UNTIL THE END OF THE FLASHING...
Do not ask me why...the above steps worked for my 10 unit...
Mission accomplished....
hschroyen