Tiger Sport Losing Rear Brake.

Yes, in the mountains in Spain on my 1050 Sprint ST. Replace the fluid and bleed.

 

I overheated the rear brake on the Honda NC750X I was riding down a very steep hair pinned mountain on Gran Canaria and lost it temporarily. Scared myself .

 

You're braking for too long and boiling the fluid.
Brake fluid (most common) is hygroscopic, meaning it absorbs water, obviously the system can't be totally sealed otherwise pad wear would create a vacuum.

Flush and re-bleed with new.

In future practice more engine braking and heavier, shorter, brake applications rather than dragging them for extended periods.

 

@Gern Pretty much answered for you on this one. Also check for leaks. But i would suspect you boiled the fluid.

 

Use more front brake which is where most of the weight transfers to under braking. That's why there are two discs there. You really shouldn't be using the rear enough to heat it that much.
Also, at two years old, your brake fluid should be changed.