Note: I’m at my beginner and just started using Figma.
I actually worked on it until I found a solution after fixing the constraints you suggested to bottom but the footer still wasn’t showing up when I tested my prototype.
So, I figured that it must be an issue with one of the components within the folder. What happens was one of the components within the footer folder was not set to to vertical scrolling. You can check this by:
-selecting the main component that you used to create the instance from.
-Enter prototype mode
-under the overflow scrolling menu if it says no scrolling, change that to vertical or horizontal scrolling.
If the primary component is not set to scrolling then it won’t appear when you check the “Fix position when scrolling box” under the constraints menu when in design mode.
Hope this helps anyone who is having trouble with this.