Invoices disappearing in MYOB

Hi,

Have had a issue pop up recently, where an invoice that has been sent to a customer has disappeared out of our system.
Initally we though it had been deleated, however when looking at adjustments that were made for the invoice, none of those values are over when they should be, and all the items that were stocked and should have been taken out of stock, are still in stock.

We tried to manually input the invoice, however we have been getting the error message that the invoice number is in use, and we cannot use it again.
I have also found the invoice in sent emails through myob, however it comes up "you do not have permission to view the transaction or its been deleated"
I have also looked though the journal security audit report, however I have been able to find the specific transaction.

I would like to find out what happended to this invoice, mostly too see if is an isolated incident, an employee error, or somthing else.
Any feedback on where I should look further would be appricated.