Yes the humidity is likely the cause of all your problems. @ 80% humidity I'd expect a very poor burn, not to mention mold any minute now. The tobacco is simply not as combustible as it should be at that humidity level.

Because the tobacco was not burning properly you likely had a build up of smoke and tar from what little you did burn which is the likely cause of the bitter or sour taste in particular. The wrappers didn't have signs of mold on them did they?