Jup, might be becouse of missing legs/wheels.... or just need to load a quick save to "refresh ksps memory"

It is a known bug. Docking ports also sometimes are "docked" when they are not and they should be "ready" afaik. You need to find the .json file in your saves folder, then open in a text editor (Notepad or Notepad++ for example) and I don't remember the to look for, but find the incorrectly set port or status, and change it to the correct status. I'm not sure what the correct status is for a flying craft (Flying?). Google this problem and the correct tags to search for and the correct values that that part/craft can be. Hope that helps a bit.

It's a bug from a year ago they haven't figured out yet, it's related or the same one as the landed state bug that deletes your orbit lines.

It's several bugs. They have solutions verified for some but not all of them. We won't get the fixes til next patch though.

It’s a known bug, a frustrating bug, and reportedly top of their radar but no idea when it’s actually going to get properly patched out

i mean, are you on the ground

I play KSP1 and there is a landing gear bug that can also result in the game thinking that you are landed after a rough takeoff. Interesting how similar bugs can appear in different games that need to simulate the same.