somehow water got in the assembly and it has no way to get out.
when the bike is cold it condenses into water where you cant see it. When you park the bike in the sun it evaporates from the internal parts and condenses on the glass.
I think if you take it off and give it a chance to dry out inside it would be okay. Not sure what you would have to do to open it to let the moisture out, if just taking it off the tank would be enough (maybe not)
or if you would have to disassemble it a little further.
That also begs the question of how the water got in there - a bad seal or o-ring someplace....
if you do take it all apart, putting a bag of desiccant in there where you wont see it would help prevent it from happening again.