the pitch stop mount issue is supposedly fixed on model with manufacturing dates 06/2016 and newer. The mount thickness was increased from 1mm to 2mm and I believe they have additional spot welds.
I read this information in the most recent TSB which was published in january of this year(or something recent). So basically it SHOULD be fixed in the MY2017 cars.
as far as I understand, this is a problem in the VA's because they reduced the thickness of the mount. there's speculation that this in addition to the engine/transmission mounts being softer/more compliant than previous generations is the root cause.
I'm still debating if I want to do change the pitch stop on my '17 CVT WRX...I've seen how much movement the drivetrain has from factory but not sure anything short of motor mounts will be of benefit (there's no upgraded transmission mount for the CVT)
edit: ....crap I just realized this is my first post here and I'm sitting here giving important information with zero credibility lol. Sorry all. I'm not sure if I'm allowed to post links to things but I found the TSB by googling "Pitch Stop Mount WRX TSB" and there's a link to subispeed which is a PDF of the TSB dated January 23, 2017
Edit 2: taken from the TSB
The part number for the new pitching Stopper bracket is: 51234VA0809P. The new bracket is easily
identified as the thickness of the material used has been changed from 1mm to 2mm. There is also a
7/16” hole near the top on the driver’s side of the bracket above the weld nut for identification