Screen mirroring a mac via apple tv stops working after about 15 mins, continues to show on mac

[KarenF]

I screen mirror a zoom class from my mac onto a Pioneer tv via an apple tv unit. This works fine although the sound does not come through the tv. 

The big problem is that after about 15 mins the tv shuts down despite the zoom meeting continuing to show on the mac.

It seems to be a zoom thing, because if the mac is showing a youtube video, the sound comes through ok and the screen mirroring doesn't shut down.

Any thoughts anyone, please!