I just discovered that when I tap the send button on WhatsApp the music stops for while. Actually it doesn't stop. The headsets goes silence for a second and then continues normally. The same thing happens when somebody sends a message to me. But, it doesn't happen when I receive messages while I'm on another screen. For example, at the very moment I'm writing this question and music plays on. I saw that I'm gathering new messages on notification area, but no problem occurs.
I'm using JBL TUNE 600BTNC Bluetooth headset.
My phone is Realme 3 Pro.
Android version is 9.
The music players I tried are VLC and PowerAmp.