Has anyone experienced major cycle length changes?

My average cycle length is 24 days. Shortest I ever had being 21 days and longest being 27. So this month according to glow and another app they think I ovulated way late due to bbt Cd17 and that I'm going to have a 31 day cycle? Now I'm so confused cause I think I'm having period cramps but if in nit due AF till 10th then wtf or will I bleed on 3rd like 24 day petter will predict. Has anyone experienced a significant shift like this.