Official comment

It must have been a lower light situation or the approach to the starting point must have been dark because the app detected that longer exposure times were being used which can cause motion blur. This is there to keep your images from becoming a streaky mess but you can turn it off in the Settings if you want.
1. You can hit the unlock button to clear any past progress.
2. The app wants to match the flight speed of the previous flights because the images are taken with a camera with a rolling shutter. This makes it so the footprint being imaged on the ground is stretched differently at different speeds. Mixing this stretching is not ideal and can cause processing inaccuracies. This is why we don't REALLY like people messing with the ISO settings unless they fully understand what is happening. Long exposure times leading to smear of more than 2X the GSD is the best way to ruin your whole dataset.