Hi @tobias-dahms,
Do you have UBX files? You can try converting several UBX logs to one RINEX log in RTKConv, just link to all of them in the field for input data. For it, you should specify the path in such a way: C:\...\rover\raw*.UBX.
You also can choose several files in RTKPost base and rover fields, it allows processing all RINEX logs at a time.