Hi guys, Pro1 is booting sailfish again! Thanx to all for their help. The problem was indeed just the USB3 port. After using a USB2 port, problems vanished into air and i could flash easily with fastboot. So now I have to reconfigure my device and than make a backup, which I for sure will not sacrifice for photos again. At least I backuped my pics before I did the update on devel. So no data is lost. And I just had some time wasted thanx to my stupidity.
Lesson learned