Spectrum analyzer with Python API

I am trying to follow the Spectrum Analyzer example from the example API page. However, when trying to set the rbw using the set_rbw('Minimum') method, I get the following error:

In [12]: m.set_rbw('Minimum')
InvalidParameterException                 Traceback (most recent call last)
<ipython-input-12-6099cb782cd4> in <module>
----> 1 m.set_rbw('Minimum')

~\Anaconda3\lib\site-packages\moku\instruments\_spectrumanalyzer.py in set_rbw(self, mode, rbw_value, strict)
    179             f"slot{self.slot}/{self.operation_group}",
    180             operation,
--> 181             params)
    183     def get_span(self):

~\Anaconda3\lib\site-packages\moku\session.py in func_wrapper(self, *args, **kwargs)
     15     def func_wrapper(self, *args, **kwargs):
     16         response = func(self, *args, **kwargs)
---> 17         return self.resolve(response)
     19     return func_wrapper

~\Anaconda3\lib\site-packages\moku\session.py in resolve(self, response)
    164                     return data.data
    165                 elif data.success is False:
--> 166                     self.handle_error(data.code, data.messages)
    167             else:
    168                 self.handle_http_error(response)

~\Anaconda3\lib\site-packages\moku\session.py in handle_error(code, messages)
    120             raise exceptions.NoInstrumentBitstream(messages)
    121         elif code == "INVALID_PARAM":
--> 122             raise exceptions.InvalidParameterException(messages)
    123         elif code == "INVALID_REQUEST":
    124             raise exceptions.InvalidRequestException(messages)

InvalidParameterException: ['Unable to set  to desired value. Coerced value: 21.153033']

I’m using fw=580 - in fact, I was successfully able to use this call using an earlier version of the firmware, so maybe it has something to do with an update made to this version of the fw?