with our journey with S/4 HANA Public Cloud we experienced some challenges with external and internal number ranges. As for external number ranges we couldn't use Audit report in Fiori, but only we were requesting special report from backend system, we went for some entities to internal number ranges. As you probably know they have different MM and FI document numbers.
In GL reports they are both displayed, but in some AP reports information is missing for MM document number. Example is with Manage Supplier Line Items. Unfortunately it shows only one number which is FI, but for supplier data. At the same time during creation of supplier invoice with app Create Supplier Invoice - Advanced MM number is given. How user can check supplier invoice in app Manage Supplier Line Items if he received MM number ? Today by going to other reports showing how these document numbers are matched, meaning FI number with MM. This is time consuming and not the best user experience.
I created innovation request for app Manage Supplier Line Items. If you are interested in this improvement, it would be great, if you could vote for it too. You can go there at https://influence.sap.com/sap/ino/#/idea/220089 . Required threshold for customer votes is now 8 in Finance project.
I'm also interested in your experience, how do you deal with it ?