In addition to the game displayed to the HMD, ROBLOX shows a preview of the game in VR:
I was testing controller input – nothing visual – so I had the HMD off (it’s not the most comfortable to keep on due to its weight & inconvenient to switch back and forth between it and Studio’s script editor), and was viewing the game through the preview. Because of that I didn’t notice the Steam overlay was open and couldn’t figure out why input wasn’t making it to ROBLOX. It’d be great if there was some sort of visual indicator like “ROBLOX is inactive” across the screen when ROBLOX isn’t the active VR process.