I have the same problem with my Garmin Drivesmart 51 LMT-S. Your advice here did not work. Basecamp says there is a problem communicating with the device. The "current.gpx" file is re-created per your instructions but it still does not work. How do you load gpx files in the Drivesmart 51 and run them? Thanks.
PS...I found that Basecamp WILL send a gpx file to the Garmin. It puts them on the memory card in Garmin\GPX. I can also manually copy them there, too. They will work when I go to Apps, Trip Planner, Saved Trips, and load them. However, I still get the above error messages when I connect the Garmin to Basecamp even though everything seems to work.