So for anybody who got stuck in this mode - 900E in device manager when plugged in.
I got to this state with Redmi Note 3 Pro after normal flash failed (while in "normal"EDL mode) for the "not enough space" error - after the error
appeared I couldn't reflash (not with Mi Flash nor with the Mi Flash Beta) and got stuck in this mode.
What DIDN'T work for me:
1. long (or very long) press on off button or any combination of the buttons.
2. "plug in USB + button combination".
3. remove battery by disconnecting the cable.
3. same as 3 for 10 sec + disconnect USB flex cable + (after connecting again all) step 2.
+ use the Xiaomi deep flash cable.
as I didn't have a cable I made a hackish cable - strip the green wire inside the USB cable and short it when first plugged in with the ground (I've used the outside metal part of the USB connector - big side - and spare wire that I've looped around the striped green wire and held it pressed to the connector with first plugging in).
+ when using the cable I've got good recognition in device manager (Qualcomm HS-USB QDLoader 9008).
+ flash using the Mi Flash again (I've used the Beta one - don't know if it matters). I've flash the Dev Global (what I wanted to flash to begin with)
+ after successful flash (for me it took about 16 min) it will just say successful flash and do nothing. if you will re-plug the cable (without shorting it) it will ID again as 900E . BUT! now you can just hold the power button for 10 sec or so and SUCCESS! the device will reboot and all is good in the world!