What could cause Command-Tab task switching to get "stuck"?

Solution 1:

Just had the same issue.

Turns out it is because I've got my mouse in my bag and it's still connected to the bluetooth dongle on the machine. So essentially is the mouse.

As soon as I disconnected the mouse the issue went away.

Solution 2:

Had the same issue today - almost 6 years later!

Couldn't find any workable solution online. I had already tried restarting and logging into another account with no help.

Finally reached out to the apple support. They got me to do a safe boot (https://support.apple.com/en-us/HT201262).

The problem wasn't there in safe boot mode. Then, booted back to normal mode - and the problem was gone there as well!