Check the wiring on wear and tear. These look a lot like the symptoms I had. After a while I ended up with a fuse blowing caused by a bear wire rubbing against the frame. It's not related to a specific speed but to a certain degree of vibration... I guess.. Just like you I, at first, thought it had to do with humidity...
There's a thread somewhere with nice pictures.
Ah... here they are (but in your case it could be on a different location):
It is more likely to happen if your bike has done several tens of thousand km's.
HJ