I checked the wifi of my RaspBerryPi by booting a new “Raspberry Pi OS” fresh downloaded from https://www.raspberrypi.org/downloads/ and surprising: Wifi (with interface wlan0) starts pretty out of the box! After all I downloaded the newest version of Volumio (current 2.777 - image file volumio-2.777-2020-05-25-pi.img.zip) put it on the SD card and started Volumio from scratch. And: The same issue: wifi / wlan does not work, O get always the same error:
May 30 19:00:57 volumio2 wpa_supplicant[732]: wlan0: Failed to initiate sched scan
May 30 19:01:03 volumio2 wpa_supplicant[732]: wlan0: CTRL-EVENT-SSID-REENABLED id=0 ssid=“MySSID”
May 30 19:01:03 volumio2 wpa_supplicant[732]: wlan0: Trying to associate with SSID ‘MySSID’
May 30 19:01:04 volumio2 wpa_supplicant[732]: wlan0: CTRL-EVENT-ASSOC-REJECT bssid=00:00:00:00:00:00 status_code=16
May 30 19:01:04 volumio2 wpa_supplicant[732]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=0 ssid=“MySSID” auth_failures=7 duration=90 reason=CONN_FAILED
I found an older posting: Can't find my WLAN with similar issues and the same wlan router (Fritzbox). I’m starting to suspect that somehow Volumio has wifi issues with Fritzbox routers?