Doing some walking around in Gilded Vale (don't worry, no save/reloading unless I'm inside ) when I decided to toggle Eder's Defender mode on and off, y'know, like you do... and there was no fun shieldy FX or shield shattery FX. Made me sad.
I'll try and watch to see if I can notice any other specific triggers for this bug, or if it persists. I'm not sure exactly when it started - could be an area-dependent thing. Will update if I find anything else out.