It's unclear if that is a limitation of the Oceanic app or the sensors. The watch waterproofing is rated to 100m. +40 meters is beyond the limits of recreational diving so it would make sense that the app no longer gives you decompression info beyond that range.

When freediving, 40 meters is not unusually deep. Many divers can get past 30m after a long weekend of training. I'd be disappointed if a different app couldn't track beyond that limit.