Adobe Acrobat Pro DC Connected Lines Issue

Hi Can anyone help please?

I am using Adobe Acrobat Pro DC and the connected lines function has stopped working properly. I can draw lines however, if i need to delete them i cant now. Before i used to be able to highlight the line and simply press delete or backspace and they would go. Now i get lots of comment boxes come up and cant delete at all. 

I also cant change the lines once drawn. I used to be able to drag the little boxes at the line intersections and move them.

What is the problem please? I bought this programme at great expense to have this function.

I also tried the Never option as above but it made no difference.

Thanyou

adam