Live TV stops after a few seconds, or repeats the same half minute

This has one common cause: the subscription's stream is already in use somewhere else. Most subscriptions allow one at a time. When a second device asks, some providers hand out a few seconds of picture rather than refusing outright, which looks exactly like this.

What to check

1. Is the same subscription playing on another television, phone or box? Close it there.
2. Is one of your own booked recordings running? Settings → Scheduled recordings shows what is due.
3. Did the app leave a stream open elsewhere in the house? Restarting the app on the other device releases it.

Confirming it

Turn on Settings → Playback → Show stream diagnostics. A short line appears under the channel name while a live channel plays. If it reads live=no with a window of half a minute or so, your provider handed out a fixed clip instead of a continuous stream — which is what a subscription already in use looks like. Turn it back off once things behave.

If none of that applies, the connection itself may be dropping. The app reconnects on its own several times before giving up, so a channel that keeps stopping and restarting points at the network between you and your provider rather than at the app.