I'm glad I saw this post.
I had a similar problem yesterday and today for the first time.
I've owned my 2012 Overland for a few months and haven't had a single problem or warning message. Saturday I took it to the dealership for the first oil change. Then Sunday night, for the first time I get a warning message that states "Blind Spot Detection Unavailable". I also noticed the yellow triangle on the passenger side mirror was illuminated and stayed that way. I arrived at my destination and shut the truck off. When I returned and restarted my JGC the error message was gone the Blind Spot Detection system worked correctly.
Then, again this morning (Monday) it happened again. This time I also discovered that I couldn't roll down either of my front windows while this fault was happening. The yellow triangle on the passenger mirror again lit up and stayed that way. I had to exit my vehicle to open a security gate and when I got back inside everything was back to normal.
I haven't reported this problem to the dealership yet. I'm hoping it is just something like the passenger door not being fully closed. If it happens again I'll be contacting my dealership but I don't know if I'll trust them to fix a problem that I believe they might have caused.