If you have a customer with only some delivery notes to him, you can delete the customer and the delivery notes will remain orphans
I can reproduce this bug.
Of note, when the orphaned delivery note is viewed, a UUID shows in the
Customer field on the Edit screen. But the View screen shows nothing where the customer should be.
Exactly the same behavior applies to suppliers and goods receipts. I have edited the subject of this thread accordingly.
Thanks. Fixed in the latest version (19.11.72)