Hi Ced, for a case like you show there a better way is to select the top face and then run the Fillet command. When Fillet is given a face as input it will target all the edges of that face.

For the loop selection, is it possible you have some tiny unselected edge in between those 2 you have selected? You need to have 2 consecutive edges selected for it to work. Either that or do you maybe have a standalone curve object selected there instead of edge sub-objects?

If you can post the 3DM file you show there I could probably give you some better information.

- Michael