I got the exact same thing to start with.
Keep pushing the installation after the recovery process has completed.
That first reboot after the recovery is when to push the launcher.
I found mine took after the spinning Sonoff graphic and just as CAST comes up on the screen and it was too late once the eWelink log comes up.
I hope this narrows the timing for you.
Once pushed I completed the eWelink setup with the QR code and went to About and selected Reboot.
On the next load it gave me the option to choose launcher. I selected Always.
Once loaded in, I went to About and activated Dev mode (blah blah, you get this bit).
In the Dev Mode menu, I enabled USB debugging.
I then turned it off and put it all back together.
Now it is back together, I can continue with the great doc from blakadder using the connect command.
This allows you to continue the setup over the air and has no need for USB cables.
In summary, spam it, it will take I promise as it worked for me last night.
Spent hours on making this work, and thanks to Filya75, I had this nailed in an hour.