Terrain Moves upon play.

Hello there!
I'm trying to apply to a game design school and they recommended me to try make somethingin in Unity or Unreal engine. So i decided to create a small 3d game, however it worked fine for a while but all of a sudden for some reason, when i hitt the play button (Test) the whole terrain moves location wish leaves all the objects hanging in the air and when i stop the play test it moves back to its original location.

I'm completely new to unity so I expect doing alot of stuff wrong.

 

Select the Terrain and click the "Static" button in the Inspector. This normally shouldn't be happening so I suspect you really messed something up.

 

same problem i discover at some moment i just put a nav mesh agent on my terrain by mistake. fixed now