RPI-3/Volumio does not memorize router connection

I dont know if it has to do with but right after securing my configuration with the plugin Backup & Restore (backup file was generated and it is ok) my RPI-3 stopped working and I had to reflash, not a big thing. I went through the wizard, connected with the router/password and unit started again.

Problem now is that it does not retain the router connection, its own Volumio-SSID starts and I can connect again with the router/password, it starts again and again the same … and so on…

What now … any ideas?