Sound not playing on lock screen

Hello,

Today I have had a problem where I am playing a radio station in a tab on Chrome and when I lock my screen the sound stops. 

It didn't used to do this, before I used to lock my screen and the sound would continue to play.

I am connected to the office bluetooth speakers, I'm not sure if this makes a difference but I was connected to the same speakers before when there was no issue. 

Is there a way to get the sound to continue playing when I lock my screen as it used to do before? I can't find any answers when I try to google. 

Thank you!