Unfortunately this thread is closed: https://forums.garmin.com/showthread.php?370859-How-to-deal-with-custom-route-creation-interruption-in-Base-Camp
But I have exactly the same problem and actually I was quite happy that I found the posting from Lenny-FL, but still it does not work.
While on my test route the grey circle appears properly when I want to continue my (interrupted) route, on my "real" route this big grey circle refuses to appear, very stubborn.
When I use the "insert" tool and hover over the last point of the route (where I need to continue), insted of the big grey circle only the connection between two points is shown. But I don't want to insert an additional point between two existing points, I need to continue my route.
Working on test route:
Not working on my "real" route:
Tried with the cursor from all directions. Nope. Frustrated. Feeling stupid.
Thanks for an advice.