Based on the feedback from our users, we have purposefully decided to keep the phone screen alive if the main player is being shown inside the Snipd app.
The idea behind this is to let users easily hit the "Create snip" button while listening to a podcast.
If you do not like this behaviour, the easiest way to not have this happen is to minimise the main player or use the phone's physical sleep button. Further, if you'd like to have a different behaviour, it would be great, if you reached out and let us know :)