Port Placement

Hi,

When trying to place a port on the front face of my speaker box, I am unable to select the bottom edge.

 I have tried changing the butt joint type for the edge (as mentioned in another question about port placement) but this makes no difference.

Project is here: https://speakerboxlite.com/project-info/cc389fb98c676545e656b384a1f170c5d45f5473fd386a66843c45026afb8010

Any ideas would be appreciated!

Duncan