App Switcher (cmd tab) not working properly

Many thanks Rings o'Neptune, this helped (and I sympathise with your side remark in the first item of "Chapter 2", too)

My small addendum to Chapter 3:

• In addition to ⌘-tab, also neither F3 nor Fn-F3 were working for me -- I got to the survey of desktops by swiping-up with 4 fingers (activated gesture) and used that to simply switch to the other of the two open desktops (both being actively used, the second desktop had been created automatically upon maximising (green button) a window): this desktop switching turned out to be sufficient to bring things back to normal
• Along with ⌘-tab, F3 also working again

Configuration: Macbook Pro (Retina 15" mid 2015), running OS X 10.11.6 (15G1217)

Hi, mashinhead.

Thank you for visiting Apple Support Communities.

I understand that you upgraded your Mac to El Capitan and now are unable to use the Command + Tab option. This feature is still available, so I would need a little more information to better assist you. Are you using a third-party keyboard and what type of Mac are you using? In the interim, try resetting the SMC, NVRAM and go through the troubleshooting steps in the last article below.

Resetting the System Management Controller (SMC) on your Mac

How to Reset NVRAM on your Mac

Troubleshooting wireless mouse and keyboard issues

Cheers

Hi Mashinhead i had this same problem. The solution for me was: Using the F3 function ( show all opened apps ) you will move the mouse to the top of the screen. There you will see the open app and the Desktops ( if you have more than one ). Now you just need drag the apps out of your current desktop for inside the screen, and the cmd+tab may work now.

Variation on a theme here, with additional clarity on the solution.

Chapter 1: In the Beginning

• original upgrade Yo -> El Cap was fine.
• The subject issue emerged during a subsequent update

Chapter 2: The Tension Builds

• On arrival at this site -- and with all due respect to him -- I find Jason269's suggestion very unsavory.
• RLira's suggest is so much more appealing, but I cannot figure out what in the world she and/or he means by

... drag the apps out of your current desktop for inside the screen....

Further, F3 does nothing for me!

Chapter 3: Climax & Dénouement

• I determine that RLira meant fn-F3. This key action does something that lines up with the first part of her and/or his description. I find I have 3 desktops.
  • hit Fn-F3
  • Mouse over the "banner bar" at the top of the display & keep the mouse there. The "banner bar" will expand to show a postage-stamp-sized image of each desktop with its contents.
  • Click on a postage-stamp-sized desktop image to visit another desktop.
• Still making no sense of "drag the apps for inside the screen," I check the other 2 desktops & find no hidden apps there.
• Playing a hunch on the problem's association with multiple desktops, I delete the 2 desktops that I believe I've never used.

  Mouse over one of the postage-stamp-sized desktop images, and an 'X' in a circle will appear at the top left of the postage stamp. Click that 'X' widget to delete that desktop.

• I return to my original desktop, and find ⌘-tab is back to it's old sane self again. Just. Like. That.