Try launching the game through “Launch SteamVR” or the “Games” menu within VD’s main menu inside the headset (both can be found by clicking hamburger button on your left controller with VD running). Launching your game through VD’s mirrored desktop does nothing.
I wonder if it has something to do with PoE’s recently added Vulkan support (I’m running it on DirectX)? Pity that their frequent patching breaks vorpx so much, PoE in stereoscopic 3D looks so dope on YouTube.