I don't know if this will discourage or encourage you but ... if your scale isn't working now, it probably wasn't working 6 weeks ago either. A ten pound difference is probably a matter of a messed up set point. If that's true, then your weight might have been higher to begin with, and that 20 pound weight loss is real.
I would get some new batteries and try them, try a new scale, try the scale in various spots in the house (mine is off if the ground isn't perfect level), and start taking your measurements since they can show fat loss even when the scale doesn't.
And cleancowgirl is right, having access to a medical grade scale you can use is great too. I don't use the one at my gym because it's out in public (eep!) but when I go to the doctor I always check that the weight there is the same at home.
Journey Started - 7/8/2013 @233; ONEderland - 9/26/2013; Lowest weight - 12/20/2014 @177
Journey Restarted - 9/10/2014 @200