Gear VR Dynamic Materials + UMG

I’m using UMG to do a circular HUD element [(like this one)][1] for my Gear VR project. I have a PNG texture of a circle with a transparent background, which [fits all the requirements outlined here:][2] it’s 1024x1024, uses Default compression settings, etc. If I create a 3D UMG widget with this texture and attach it to my pawn, everything works fine.

Now: I create a Dynamic Material that masks out different parts of this circle based on a parameter. I change the UMG widget’s Brush Image to an instance of this dynamic material, and store it in my pawn BP. Everything looks good in VR Preview on my Oculus Rift: I now have a circular HUD element that I can set the progress of dynamically.

However, in the Gear VR, the HUD looks static-y and distorted. Is there an issue affecting Dynamic Material-based UMG widgets on the Gear VR, which for some reason does not affect texture-based UMG widgets?

EDIT: I’ve tried packaging with different texture settings (ETC1, etc.), nothing fixes it. Here’s how it looks on the Rift in VR Preview:

And here’s how it looks on the phone in Gear VR mode (sorry for crappy screenshot):