Lowrance has not been known, at least in motorcycle circles, as a customer-friendly company. Weigh your purchase decision by that. I think my iWay 500c is among the best hardware out there, but the software that drives it needs a LOT of work, but then so do most of them.
Your screen might need cleaning around the seams. Carefully separate the cover, taking care not to damage any of the seals, and clean the whole face of the screen, then reassemble. This has helped others with the problem you describe.