Hi, yesterday after 1-hour flight landing flight log continued to count for another 20 minutes when airplane was at the parking. As a result in the log I had wrong landing time (+ 20 min), wrong flight time and wrong average speed.

I understand log starts and stops automatically depending on speed.

Is there a way to force it to stop manually or at least to see if it stopped or not?

Flight logging stops when your speed drops below 10 knots and stays there for at least 20 seconds, as I recall. This is quite easy to test in a car.