You wouldn’t change your oil while on the highway.
Or change the materials in a house half-built with a few days to go.
Or start teaching a new lesson when the first one isn’t finished.
Or turn on the dishwasher when only a few dishes are in it?
Then why are you running a Sprint Retrospective while your team is working on delivering said work?
They are in a different mindset, a different zone, a different area of delivery altogether.
Wait until the sprint is over, give people time to collect their thoughts, then ask the questions that you want to get the real answers too.