Elevation plot on courses sent from the basecamp to the watch showing flat line.

Basecamp 4.8.12 (Mac version)

Watch software 15.10 (9e6214b)

I noticed my watch doesn't display courses' elevation plot correctly so I created a simple route with Basecamp and sent to my watch to test. I confirm there's a valid elevation graph for the route I created with the Basecamp software. After I sent the route to the watch, 'Navigation -> Course -> MY_COURSE -> Elevation Plot` then it shows flat line graph.

If I hike using this route, my watch shows a flat line for the remaining ascent data. However watch correctly records actual elevation profile during hike activity.

Anyone know how to solve this?