Modems show offline even when though connected and online

Our modems seem to pretty consistently report offline even though they are online. I first saw this with an ocw box at southwark:

<img width="771" height="470" alt="Image" src="https://github.com/user-attachments/assets/96f5f3af-d8fc-4125-bf10-603d43d3e9d2" />