I don't know if this is a known issue but there is a common conflict that is generated due to a duplicate entity.
Method will show a warning if you attempt to save a duplicate entity. For example, if a customer named "Practice Test" already exists in Method and you attempt to enter a new customer named "Practice Test", method will show the warning the same as QuickBooks.
The problem is, if a customer named "Practice Test" already exists in Method and you enter a new customer named "Test, Practice" (or vice versa), method accepts this but a conflict is created because QuickBooks sees this as a duplicate customer/entity. The problem is then compounded because the Method user can then use this customer to create invoices, work orders, etc. When the conflict is resolved typically by deleting the duplicate the existing invoices, work orders, etc are orphaned.