I've found the solution...
In my document generation microflow, I was committing the FileDocument object, but not the list - which I loop through to associate to said Document. After committing the list as well as the FileDocument, it now returns data just fine.
I'm still not sure why I don't need to commit the list to just return the associated list, unordered in my document just fine, so if anyone knows why that might be the case let me know!
I would make 'tripple' sure that the association project_printreport is filled with a list of projects(and not for example with one object). If that is indeed the case then the sort should work normally.
If it still does not you could then fill the datagradid with a microflow datasource and sort the data in this microflow. You could debug this as well to double check if your sort works.
I've found the solution...
In my document generation microflow, I was committing the FileDocument object, but not the list - which I loop through to associate to said Document. After committing the list as well as the FileDocument, it now returns data just fine.
I'm still not sure why I don't need to commit the list to just return the associated list, unordered in my document just fine, so if anyone knows why that might be the case let me know!