Application switcher disappears behind windows

Title says it all.

Instead of popping out in front of all the open windows, the task switcher is stuck in the back. At first, I thought it just didn't work - and then I closed some of the windows, I saw it was just kinda stuck in the back.

EDIT 07.12.2017: Tried the fixes in the comments and answer below, no cigar.

I solved it by using CompizConfig Settings Manager. Go to Window Management and enable Application Switcher. By doing so I got a popup telling me that there were conflicting bindings with another plugin. Click Resolve conflicts, and set x anyway on the following dialogs.

I don't know the cause - but a reboot fixed it for me. I'm sure lighter-weight solutions must be possible.

Looking forward to someone providing a better answer.

I've seen this issue several times, including just this morning.

Based on the discussion here: https://ubuntuforums.org/showthread.php?t=1860967, I tried unity --replace from the command line.

The good news is that it fixed the issue; the bad news is it's only a bit less drastic than logging out or rebooting; it immediately killed almost all my GUI apps (only gedit and the terminal window remained).

Incidentally, there was a somewhat nonsensical message in the terminal: WARNING: This is for compatibility with other desktop interfaces please use unity without --replace.

I have no idea what that means, or what we should type instead. But this command did put my task switcher back on top.