IPhone 7 allowed Calm app to continue playing on lock but iPhone 12 pro doesn’t

Hi, I had an iPhone 7 until recently upgrading to an iPhone 12 Pro.

previously with the 7 I could play the Calm app and it would continue even when the screen auto locked. The iPhone 12 pro doesn’t allow it to continue when the screen locks however.

i know I could disable the auto screen lock, but I would prefer not to amd just wondered why this would be necessary anyway. Is there something I can do to stop it halting the app just because the screen auto locks?

i’ve tried ensuring background app refresh is on for the app - but this doesn’t make any difference.

can anyone help with this? Thanks.