Inside of the Off Page Connector Create Connection dialogue box you may only see the drawing listed that you are currently working in and not the drawing you are trying to connect to.
Luckily the solution to this is typically quite simple and easily overlooked. The line number property is the primary field that is used when making these connections and if both sides have the line number property filled out this process wont work and the connection box will display like the above image.
If you clear the line size field on the side you want to change/update and go back in to create a connection.
The Off Page Connector drawing selection list should now display the drawing and Off Page Connector that you are looking for.
