Not sure exactly how this happened, but reporting as a potential edge case bug.
Instance - I have the YouTube app installed on one of my profiles. I also have it set to be available to play on lock screen. From what I remember, I was watching a YouTube video and then paused it.
Then switched to another profile where YouTube is not installed. Did some things on that profile, click through some apps, etc. Locked my phone. An hour later with my phone still locked on that same profile without the YouTube app installed, the YouTube video I was watching started playing through my phone speakers. The video was not on my lock screen, however. There was no URL to the video I shared in any other apps on this profile, browser was clear (delete data on exit): no direct access to YouTube whatsoever. I switched back to the profile that I had YouTube installed and did see the video on the lock screen, but it was not plaiying.
Anyhow, very strange has never happened before. Mainly pointing this out because my belief was there was app isolation between profiles.