Reauthorisation prompt appeared this morning - what actually triggers it?

Routine in your case, and the ten seconds is the whole point of the prompt existing. What it means: the permission we hold to talk to Google Ads on your behalf stopped working, so rather than quietly failing every update until somebody noticed the data was stale, we ask you to grant it again. The usual causes, and none of them is anything you did wrong: A password change on the Google account, which invalidates existing permissions. Someone revoking third-party access in their Google security settings, often during a routine tidy-up without realising what it was attached to. Google expiring the permission on its own, which happens occasionally. A change to which manager account the Ads account sits under. What matters for your client conversation: while the prompt is showing, updates are paused rather than lost. Reconnecting picks up everything that was missed, so there's no gap in the history afterwards. The reason we surface it as a prompt rather than an email is that it's fixable in seconds by whoever is already looking at the screen.

Nothing lost is the part client will care about. Thank you.