According the Paolo entry, the trouble may come from the ramp used to perform the transition from the standard filter to the boost filter .

I put back the ramp of 10ms with a sine form ,

• at the first trial, the transistion to the boost succeeded
• at the second trial, the transition failed

Then I reduce the transition time to 5ms

• at the first trial, the transistion to the boost succeeded
• at the second trial, the transition succeeded too

The ramp was reduced and set to zero due to somes troubles observed and to some lack of knowledge .

According  Paolo, the ramp is used to perform the switch between the 2 filters on the Sc_MC DSP too. As there is a delay between the SSFS rtpc and the Sc_MC DSP of 200us or 300us (2 or 3 10KHz cycles)  the ramp must be slow compared to the  delay.

According Paolo it could be useful to have the starting to the boost transition only when the error signal is close to zero