If a note Off is delayed, then there is a moment that two notes are ON. This might cause a mini legato / glide in Respiro.

If the Respiro note transition is set to Synth mode then you will have less pops versus when you use the Real mode.

I would need to dig into the Sylphyo to understand the way it deals with key glitches. But typically when using certain fingering transitions, glitches can occurs due to the changing keystroke (not all fingers in sync). I think this is why the Key / Reaction time parameter exist. Typically keystrokes less than 20ms are glitches. Therefore setting this value to 1ms will probably not filter glitches keystrokes and provide a more snappy response to your fingering BUT it demands that you master your fingering technique...Respiro is responding super fast to note changes and a glitch note during playing can result in a create a pop.

With other words, if you set the reaction time to 1ms, then I would advice Respiro in Synth Mode and increase the value till pops are gone...

Hope this helps ;-)