Why does Instagram interrupt my Deezer playlist?

Scenario:

• My S7 is playing a Deezer playlist.  I’m using my Samsung S21 to control the S7 using Deezer connect
• I have my S21 screen open; I open Instagram and browse through a few photos
• I play a video with audio.  My Deezer playlist cuts out while I listen to the audio on my S21
• When I exit Instagram, or move to another photo without audio, my playlist sometimes resumes (or I have to press play again for it to resume)

Why would any app playing audio on one device interrupt the audio on another device?!

I just tested this with a browser playing a video.  The same thing happens.

Surely this is not expected behaviour?