Circuit Board works when dry but not when humidity present

I have a circuit board that works perfectly when the air is completely dry, but when the humidity gets high, the board will not work properly. The board is fully coated, but somewhere there is a break in the coating.
Also, the circuit board is outside and covered with a material like rubberized varnish.
What do you recommend to spray or coat this circuit board to prevent moisture from getting into it?
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The problem may or may not be associated with the components on the board or the board itself. Try the recommendations below first, then check for cracks or fractures in the board.
You mentioned that there is a rubberized varnish. If there is a break in the coating and the moisture is getting into this break, seal the surace with CircuitSealer, a conformal coating.
Applying any solvent and most chemicals to varnish, may soften it, and that includes our DeoxIT® contact cleaner, DeoxIT® GOLD (formerly ProGold), CaiKleen, etc.
To prevent the connections from shorting (from dust/dirt mixed with humidity), clean all the connections with DeoxIT® GOLD.