While debugging I’ve determined that this issue only exists when using Single Pass Stereoscopic rendering. It and some other ‘Right eye only’ bugs in VR appear to not exist when instanced stereo is turned off.
Most paradoxically, in shipping builds of our testing scene, instanced stereo actually performs worse with a 5.3-6.6ms frame time as opposed to 5.2-5.8ms when it is turned off so something’s broken here.