Hey there NickyS1
I had the same issue with debtor invoices "disappearing"
Unlike you. I am using Edge and changing my browser to Firefox fixed my problem.
MYOB support played the usual tune regarding clearing the Edge cache, disabling extensions etc., but Edge refused to work as expected.
A few days ago, I decided to clear the Edge cache again, but the problem remained.
On a whim I then cleared every one of the MYOB only cookies in Edge and magically I can now view all of my debtor invoices again.
I hope that this solution is shared by MYOB support.