No, you don't need to log engine start if you don't want to. So, you logged Off Blocks, then what happened? Could you describe the rest of your flight and what your log looks like, compared to what you expected it to look like? You could send your log to us (at customer support) for us to inspect if you think something has gone awry.

You may benefit from referring to the manual regarding to how SkyDemon logs flights. In a nutshell, if you don't do anything explicit regarding logging, SkyDemon will automatically detect when you've taken off and when you've landed, so your flight will be logged. If you do something explicit, which means you tell SkyDemon when you've started your engine or logged off blocks, then you'll also need to tell us when the opposite happens at the end of your flight. It sounds like perhaps you didn't do anything explicit and therefore SkyDemon stopped logging when it detected you'd landed.

What actually happens with SkyDemon during the flight? Is it still running and navigating as normal?

One of the things I use skydemon for is to log my flights during  Paradrop operations, so that I can check how efficient I was flying that day. Up until March 2024 , it would do this continuously from the moment I clicked on the log engine start, up until the moment I clicked on engine shutdown. The time in between could be anything between 20 minutes and 2hours. But since the middle of April, for some reason Skydemon just stops logging after about 33-39 minutes which is usually in flight.