(In reply to John Brooks from comment #5)
> The firmware from comment #3 was distributed in linux-firmware starting with
> commit 5e6165a8705613646c9a5a282f0a7243fe5dafdc
> (https://git.kernel.org/cgit/linux/kernel/git/firmware/linux-firmware.git/
> commit/?id=5e6165a8705613646c9a5a282f0a7243fe5dafdc). Which corresponds to
> Ubuntu's linux-firmware package version 1.158, released on May 6, 2016.
> 
> People who already had this firmware would not experience the regression,
> which could explain the mixed reports of reproducibility.

The latest firmware from upstream linux-firmware.git matches what Leo posted. 
I think you just need to update your firmware from linux-firmware.git and
Ubuntu needs to update as well if they haven't already.