Whenever I click “start” on my “user interface” scene, my character on my game slowly goes down… but then it stops… how do I get rid of that “moving downward” motion. Can anyone please help me on this?
TLDR, your character is going down due to gravity.
On the main menu, the scene settings has gravity set to -9.8.
When you load the game scene, you are only loading the scene hierarchy which means that the scene settings of the app still has gravity set to -9.8 instead of 0
You will need to load the scene hierarchy and the scene settings. The documentation has projects and a helper script to make this much easier for you to do.