I'm having a hard time migrating from other CAD programs regarding closing sketches. My first sketch always closes like I expect. If I add a simple polygon attached to that one, I can close it by doubling a line (which seems dumb, but it does work). But then if I add a more complex neighboring polygon, I can't close it even by retracing the lines. What am I doing wrong?

https://youtu.be/ZNRU4kCXcW