I'm using a Gungnir, FWIW. And a Pro (not a Pro Plus). Have you checked your WiiM device settings to see if anything changed with the update?
Perhaps
@onlyoneme can chime in on whether he's noticed any measurable change in audio quality/distortion since the update.
I suggest opening a ticket to WiiM if you haven't already done so. If you've experienced an discernable change in audio quality, they should be able to check your device and if necessary, roll you back to an earlier firmware version.