I was getting way high readings like that on the Devil Mountain Double (Morgan Territory Climb), i.e. 245 - 255 . . . which I knew couldn't be right.
Turns out it was the strap (not the "bean") on my Garmin with two (or more) inner wires touching that can cause that (according to the Garmin Rep on the phone).
I had put the strap in the washing machine, which he told me was the problem. Washer mangles strap, wires touch (too high reading) or don't touch (too low reading).
So that might be it, (unless you always hand-wash your Garmin strap).
Rick / OCRR