Can't install working firmware after failed update

I could not find any solution to my problem. Maybe somebody knows what to do.

Something with the last firmware update of my WD My Cloud EX2 went wrong. The Power LED was blinking red and the two Drive LEDs were blinking blue very fast. This went for hours without change. The NAS was not available via LAN. I had to do a 40 seconds reset. After that I could reach the NAS again. It says it is in “Safe Mode”. The error message says “Your device firmware appears to be corrupted and your device is currently running in Safe Mode.” There is the option of a manual firmware upload and install (see picture). I tried but no change after hours of waiting. The LEDs are still blinking wildly.safemode