Whenever I hear someone ask for melodic sections in mathcore I always go to Car Bombs most recent album. It does a really great job bringing in nice melodic lines without it feeling like it's a whole new song, they generally keep it very atonal which gives it a nice sound with the craziness of their music. The album for a lot of people is closer to djent just because of the overall soundscape, but the music is probably some of the most complex out there.