Payables invoice email notifications Expiry?

It has been received from customer that the payables invoice approval -

1. By email - Approval / Reject Links aren't working on older emails, which invoice approver hadn't taken action when the email was received initially. Later when he checks and tries to approve/ reject, it seems the links aren't working to take any action which isn't reflecting to the payables invoice.
2. Notifications aren't appearing in the Bell Icon after certain period, though they were there earlier. But wasn't clicked and left as it is. However after certain days, the notifications disappears and the invoice approver reported that he couldn't action as the notification isn't available at the Bell icon.