I've upgraded Ubuntu 16.04 with Gnome Flashback to 16.10 and then to 17.04.
After that, switching keyboard layout was set to Alt+Shift, but didn't work. What works is the default Super + Space.
When I want to change in the new UI for keyboard shortcuts, I can't - it doesn't register this shortcut. It seems the shortcuts need to contain some character.
I have tried this solution but it doesn't work either. As a stopgap I am using
PS: I wonder why do things that work need to be constantly changed. Does every new version need a new way of configuring the system? And why
Alt+Shift, which worked on every system I have ever seen since Windows 3.11 in 90's, need to change now? ...