Steam overlay no longer works (Regression)

After the most recent Soldier update, controllers are no longer responsive with Proton 5.13-1-rc8 when Steam controller mapping is turned on. We were testing controllers with the same Proton build last week (Friday) and Steam controller mapping was functional then, so I am fairly confident that this is a regression with the most recent Soldier update.

I'm not sure what info would be useful for you - please let me know if there are any logs I can capture etc.

Specific testing examples: RiME, Muse Dash with Xbox1 and ps4 controllers (tested with wireless bluetooth and plugged in)