Client having issues returning signed document

Hello. We need help/advice on a client returning a document to us.

They have returned agreements to us fine last week. But this week, there are 4 outstanding documents they're completing, being notified of completion and it simply doesn't process.

They know this because after completing like usual, they have received reminders to sign and the documents haven't updated on our end either.

How do we sort this?

Thanks, Jamie