I'm running into more and more problems with the L9 as their me grows.
-Fastboot doesn't work under Windows 8.1 and 10, but under the now obsolete(for me) Windows 7, unlike my other devices, which are fine with Win 10.
-ADB seems to work, but requiring the device to be still able to boot.
-I always boot to recovery from within Android as long as the L9 ain't bricked. After a failed rom install, during which the sd card failed(could no longer write or be formatted afterwards, the last time stamps of files and folders were set during the failed install) I discovered a problem with TWRP(Artas182x's and Edwin's), which may have been present since a long time: Trying to invoke TWRP via keypress will brick the device!
So, if my P760 no longer boots, there's only download mode available, sort of the final line of defense.
-There's sort of a trick if even download mode fails: After a failed attempt unplug phone, force switch-off, if the phone is in brick state. Then switch on, force switch-off again, and only then attempt download mode again. And have patience while holding down the vol button, it might take up to 20 seconds for the phone to switch itself on into download mode. (A single forced powerdown will cause Fastboot NOT to work the next time)
But I'm absolutely clueless about the recovery issue, for now TWRP is semi-working, can only be accessed via Android, as long as the phone is fully working.
W/o Fastboot, I now have flashed stock rom several times and rooted it with Kingo rooter just to be able to run Flashify to install TWRP. If Flashify is the culprit for the TWRP issues, I could need a recommendation for a better working app.