Thanks for posting to the community and we're sorry for the issues you're having. Since you've determined that the problem is with the VLC app, please try testing different Bluetooth headphones and other mobile devices to verify the source of the issue further. Check with VLC to see if there are any relevant updates to their firmware. It's also possible the app can change where the audio is routed to (phones speaker or Bluetooth, etc.)
I've also come up with information from VLC's forums that might help you get some ideas.
Please let us your findings when you get the chance.
I have VLC on my iPhone and remember some time back that I could not hear the audio when playing video when I used anything other than the iphone internal speaker. I can't remember what changed, but videos are playing now with audio fine on my iPhone 7+. I'm thinking its was something documented in VLC that they fixed. My version of VLC is 3.1.5 (319) and I have the most up to date IOS. I don't have all my Bose stuff here, but I just checked out playing from VLC using my Revolve and my QC35ii and they both played fine. I did note that sometimes when they are connected to two devices and one of them is my Dell laptop, the laptop refused to give up the Bose and I won't hear anything on my iPhone until I disconnect the laptop.
If you have the same ios and vlc and it still doesn't work, repost here and I'll try to recreate it myself. I run my videos from the 'all files' in the media library. That is, I download all the videos to the iPhone (as I am a film composer and the videos are the films I scored). I do not use the VLC app for streaming video remotely/online.