Thank you for your quick replies.
After some investigation the cause was found.
@ freesbee; you're right, there were some small modifications made but inherent to this problem.
@ Jacobi; Thnx for your time to respond.
The cause was that the client called our customer to cancel the order. One of the staff from our customer, who has her holiday now, changed the status and never feedbacked the call and status change to other staffmembers.
This topic can be closed. Thank you for taking the time to bring feedback.