I'm currently in process of fitting some exafs data, and have encountered this issue several times.

At some point during fit one or several "guess" parameters get stuck on the initial guess value, even if that value is changed to something that has no resemblance to the data being fitted. Further changing the initial guess value has no effect, and the fit merely takes in the new value as if its been "set". The number of values affected range from 1 to all of the variables in the GDS.

Regards

Aleks