Hi Matthias,
there seems to be an error in the BRFplus when generating the code. Did you check SAP marketplace if there is a note for such an issue?
If you have no success in finding one, please raise a OSS ticket to SAP to get the issue resolved.
BTW: Your call of the function is not the optimal way how to call BRFplus and might lead to performance issues. I would recommend to take a look at the document BRFplus Basics - How to call a function and adopt the call accordingly
BR
Christian