This also happens to me if I launch again after I've landed. By changing the "situation" of the spacecraft in the save file, the issue was resolved and the maneuver nodes worked fine. I had started flying with the spacecraft before doing this, don't know if that makes a difference.
Save files are located in:
C:\Users\"user"\AppData\LocalLow\Intercept Games\Kerbal Space Program 2\Saves\SinglePlayer
please replace C: with whatever drive you've installed the game on and replace "user" with whatever your PC username is (PC login, not ksp2 username)
Scroll past the first thousand lines and look for "Situation": "Landed",
change "Landed" to "Orbiting"
Hopefully this helps people fix it until the devs can sort it properly.