Answer
Automatic resume happens only when the interruption allows it and you have not manually paused, started recording or left the chat. Starting another audio item pauses the previous one, and recording a voice message pauses playback.
Leaving the chat for another page, switching chats or signing out stops audio. Returning does not restart it. Force-closing the app also stops playback, and playback ends normally when the file finishes.
In the native Android app, a session ends after a 10-minute pause to save battery. Open the audio message to resume at its retained position. Browser audio remains subject to browser restrictions.