Unable to play this clip at this time

Most clips older than 10 days are showing a screen with a diagonal line through it icon.
When clicked I get the message “Unable to play this clip at this time.”

This used to be an intermittent problem but is now affecting the vast majority of my saved clips.
Some old clips do have a preview image but also won’t play.
I have restarted the module and ensured that the iOS app is up-to-date.

Any advice on how I can get this working again?