Something keeps randomly setting iPhone volume to 100%

Occasionally when I open the control center on my iPhone I notice that the speaker volume was set to 100%, or I'll be in public and I play a video or something and it blasts at max volume which is very annoying. I didn't do this; I suspect something is messing with the volume but I don't know what. I always keep the speaker volume all the way down. Here are my suspicions: - It seems to only happen when I'm using a bluetooth headset (AirPods) and I swap between different devices (iPhone and MacBook). - I mostly listen to Spotify. - An example: I'm listening to Spotify on my MacBook through AirPods meanwhile I'm doing something on my phone, then randomly I see the volume control slide in from the side at 100% as if I had pressed the volume up button. - The volume buttons on the side of my phone aren't broken. I really don't think this is the issue. I think Spotify might be hijacking the iPhone volume control when listening across different devices. If so, why is it doing this and can I stop it from doing that? Is there a permission or something I can revoke to prevent Spotify from doing that? iPhone 11, iOS 15.1