Created a global approval query on web client with a filter of 'pending' for status and added the Last Update Date field to this query. However, this field appears to have no data populated. We are using another query with a filter for 'approved' status. In that query the Last Update Date is populated.
When the approval request is initially created its initial status is set to "Pending". This is brand new and its status has not been altered, meaning changed to approved or reject, therefore it has no update date. Once the user changes the status to something else, saves and then sets the status back to Pending, the Query on web client will have a date under "Last Update Date" column for the pending status.