Wifi was unresponsive. So I restarted the RPI. After reboot, the UI looks like the one attached. Restarted several times with no avail. No changes were made to settings or anywhere in the system before this happened!
I have never seen behaviour like that and I’ve reinstalled countless times 
Looks like file corruption to me, you should either update or reinstall I think.
I later cleared my browser cache and it went away, but I was really taken aback by how ugly the UI had become.
I confirm that this happen. I still haven’t determine what cause this. In my case, several volumio device, with several version (from 2.266 pine64 to last RPI version). It seems this occurs when switching for a device to a other. But not sure.
I have noticed this behaviour when Volumio tries to access a disconnected peripheral. In my configuration this is a NAS.
After a short time it switches to another source.