@Tobias Reinhardt - Thanks for the question and using MS Q&A platform.
It is normal for the status of the "Receive reference data snapshot" entries to stay at "In progress" even after the reference data has been updated within Stream Analytics. This is because the status reflects the state of the reference data retrieval process, not the state of the reference data itself.
Once the reference data has been successfully retrieved, it will be used in the Stream Analytics job as expected. So, there is no issue with your input source or the Stream Analytics resource.
I hope this helps! Let me know if you have any other questions