Pro Tools 2021 playback engine assertion error, now missing interfaces
 

Pro Tools isn’t recognizing any interface beyond Pro Tools Aggregate I/O and my display monitor’s headphone output.

I have a UAD Apollo system, two x8ps and a Twin, which chain together with Thunderbolt from a CalDigit Thunderbolt Dock. The computer is a M1 Mini (Silicon). Pro Tools is a subscription and the latest version. The Thunderbolt chain goes Mac Mini > CalDigit > x8p > x8p > Twin. The dock is used mostly to get the length from the computer to the interfaces and was recommended by UAD.

I was working in Pro Tools with no issues yesterday until I rebooted to solve a hang. I opened the session again and received an assertion error (“Could not complete the Playback Engine command because Assertion in "/Users/autobld/gitlabci/PT/release/2021/r2/ProTools/DFW/Views/UMenu.MacOS.mm”). From there I tried all of these things:

* Rebooted, same issue
* Restarted Pro Tools while holding “N”—this brought up the Playback Engine but this is when all the interfaces disappeared other than the ones mentioned above
* Uninstalled and reinstalled the UA software, no change
* Reinstalled UA firmware, no change
* Deleted Pro Tools preferences, no change
* Uninstalled and reinstalled Pro Tools, no change
* Deleted Pro Tools preferences again—the assertion error came back
* Restarted Pro Tools while holding “N”, again—Playback Engine is back, all interfaces are missing again

Most of this time I was assuming the UA drivers weren’t loading correctly or there was an issue with the Thunderbolt chain but at this point I loaded Logic Pro and found that all the interfaces were recognized by and working fine in it.

At this point I’m not sure what else to try other than restoring my computer from yesterday’s backup (when everything seemed to be working) or finishing the session in Logic. Any help or guidance is greatly appreciated!

Re: Pro Tools 2021 playback engine assertion error, now missing interfaces
 

I believe I've figured this out, posting for the internet's sake—if you've had this same error pop up maybe this will help you.

TL;DR: On a Mac? Check your Audio MIDI Setup and remove any suspicious devices.

I opened a support case with Avid (which was a surprise, up until now you've had to pay to get a support code) with pretty much this same post. After a few days they told me to try deleting preferences. :rolleyes: They also mentioned deleting the com.apple.audio.audiomidisetup.plist preference file to try to rebuild the playback engine list.

I went to delete this file but didn't have it on my system. Relaunching Audio MIDI Setup recreated this file, and I could verify UA devices were being recognized as well as every other thing I had plugged in with I/O (the headphone outputs of my monitors and dock, for example). I opened Logic to double-check all these devices were appearing there, they were. I then rebooted Logic in Rosetta mode, still fine.

I went back to Audio MIDI Setup and noticed that one of my displays had no label; i.e., while every device listed had an icon followed by the name of the device and then the channel count, this particular display didn't. The device was also listed at the same place the playback engine stopped recognizing devices. Could that be confusing Pro Tools? I unplugged it, rebooted Pro Tools and…all good, no assertion error, all hardware devices appearing, no more issues. I've rebooted and opened several sessions since then and all is back to normal.

I don't know, of course, if the missing label is the issue that's tripping up Pro Tools, or if the label missing is a sign of something else wrong with the device which is tripping up Pro Tools—regardless, while other software can work around this, Pro Tools can't.

So, if you've got a similar error and the usual tricks do not work, try double-checking Audio MIDI Setup to see if there are any devices which may be triggering an error.