Several Switch players have reported this issue at this point in the game. Fortunately, they all were eventually able to proceed after multiple attempts, and after waiting a long time.
Please try again a few times and let the game sit for a while--maybe 10 minutes--each time before killing the app. Obviously the game shouldn't be taking this long to expand the island, or taking multiple tries, and we are looking into the problem, but we do think this will get you playing again sooner than waiting for us to program the fix and get the update certified by Nintendo. (Also, at the time I write this, version 1.8.0 is awaiting Nintendo's certification. The issue isn't fixed in 1.8.0; we began looking into it after work on 1.8.0 was finished.)