Hi Team -Have an issue that when changing from a Sales Order to Invoice.

Hi Team - Seem to have an issue that when changing from a Sales Order to Invoice it is not recording. It also happened when going from a sales order to a purchase order and then returning to the sales order to record information the information that was recorded previously on the sales order has disappeared. is there a reason why this is happening. The reason we find out that the sales order is remaining the same as once a week I do an audit of the outstanding sales orders that have not been converted to an invoice and we find the issue at that time.