Shooting towards the sun will nearly always produce lens flair, this is why DSLR lenses generally come with lens hoods.
Yeah i get lens flare shooting towards the sun, the difference between the monochrome sensor and the colour one could be down to the amount elements used in the lens or even the coatings on the lens can make a difference. The monochrome sensor will not require as many coatings etc because it will not suffer from chromatic aberrations.
Out of interest have you looked at the lens' while gently shaking the phone just to see if anything is loose?
Can you post a photo with the sun in front of you but without the trees? The trees aren't helping because they are effectively giving you many light sources to deal with.