If you display Solar on your console and watch it, do you get the high readings? I would see if the console is showing the solar reading first, Meteobridge might just be sending the (bogus) info along.
If you are getting readings on the console, I would start by looking for corrosion or contaminants on the "sun" input at the ISS that might be intermittently shorting the excitation voltage to the signal line.
Greg H.