Camera feeds drop out after ~20 seconds

I have several PoE CCTV cameras connected to a Synology NVR. All behave fine within the Synology NVR “app”, and also within the Reolink Client app. They all show up within Developer Tools as “idle” - which I take it to mean no movement is detected.

In my config.yaml file I just have a line with ffmpeg: and I have set up the Synology (NVR) integration.

I have two camera(?) cards on my Dashboard, and whilst they display the correct images (updated once every 10 seconds) for 20-30 seconds, after that they just show a grey box. This remains until I refresh the browser page.

Why might this be, and how can I resolve it? Is the error within HA, the camera(?) card, the ffmpeg integration, the Synology integration, or where?

TIA

Same problem here, anyone solved this?