When using the Bose QuietComfort 35 headphones and you have a Roblox game window (Studio or the Roblox player) opened, the mic channel will be activated. For anybody who has never used the mic on these headphones, it will funnel the ambient sound around you into the speaker so you know exactly what is being sent through the mic, essentially cancelling out its own noise cancellation. It also muffles audio being played through your computer. This is all fine for things like Discord Calls, but it is not something that should be activating when just trying to develop in Studio, or play a game and listen to music.
Closing all other applications that can potentially use the microphone doesn’t do anything, as well. I am on my MacBook running macOS 10.12.6, noticed this happening on my iMac running macOS 10.13.4 as well. As soon as I close Studio or Roblox player my audio goes back to normal.