volume and brightness slider stopped working

That the volume control stops working seems to be a feature not a bug. The audio is going through DisplayPort + HDMI cable to an external device which should have volume control (e.g. TV).

That the brightness slider stops working is a bug. I have the same issue on the touch bar of my 15" Macbook. When touching on it you see that it is selected but the "brightness slider animation" doesn't appear. When extending the touch bar you could still adjust brightness by tapping on the brightness buttons. Until Apple fixes the issue the only solution for me is resetting the control strip every time the issue occurs:

1. Open Terminal.app (preinstalled on your system)

2. Enter the following and hit your Return key:

killall ControlStrip

It seems a SMC reset https://support.apple.com/en-us/HT201295 fixed this issue on my Macbook. Hopefully this helps.

I'm experiencing the very same situation on a maxed-out 13" Late 2016 MBP with Touch Bar and macOS 10.12.2 (16C68). (edited)

After plugging in an HDMI display the controls stopped working; and remain non-functional after several times in sleep mode.

I was having this problem when I would connect via an HDMI cable to an external display for viewing or listening to something on external speakers that I was streaming from my 2016 MacBook Pro. Suddenly, the volume control dimmed or disappeared. Today, I went to System Preferences and selected Sound. I noticed the external display was selected and no audio was available. I switched to the Headphones option to hear through the external speakers and now I have the volume and display that I want. Next, I tried removing the Headphones and the volume automatically switched to the computer's internal speakers and played fine. When I put the external speakers back into the Headphone jack the volume automatically switched to the external speakers, as it should. I played around with this a number of times, even shutting down and disconnecting the cables to try and recreate the problem and I couldn't recreate it. So, after weeks of frustration, I currently believe I have resolved the problem with a very basic and easy solution. I hope this continues to be resolved for me, and that others with this problem find that it works for them, too!

I'm also having this issue with a "maxed out" 13' Macbook Pro with Touch Bar. I'm grateful for the terminal script, but I'm a little concerned that this is happening to a $3,000 machine. Please comment if this is happening to your computer and it's not a "maxed out" 13' MacBook Pro with Touch Bar. I've also noticed a few other problems when playing videos on the internet (odd visual distortions in the colors - though unfortunately, it has been difficult to reproduce these anomalies), and I am wondering if there is a broader issue with the machines that was have been fully upgraded. Thank you for your help.

I have the same issue on a similar !3" MacBook Pro running macOS 10.12.2 (16C67)

I have the same problem. Restarting didn't work. Has anybody figured this out?

Just have the same problem with my MacBook 13'!!!

I also have this problem (post-PRAM reset).

:..(

Much faster and reasonable fix than SMC reset. Thank you! Hope Apple figures out all these odd hardware issues with this new strip.

No need to reset SMC.

Running 'killall ControlStrip' in terminal works fine for me.

This is it. System Preferences -> Sound -> Output is the best solution. thanks !!