And here is lesson # 2 for today.
I just found this in the IKA class rules.
MATERIALS
(a) Flying lines shall be made of Dyneema, Spectra or generic brands.
(b) Bridles if used shall be made of Carbon, Kevlar, Poly-aramid,
Dyneema, Spectra or generic brands.
So it looks like it is just the lines that cant be made of Kevlar. Which does make sense because if you are close enough to cut a bridle line then you should be able to reach the kite and therefore not need to cut a line.
So i'll just STFU and stop having a convo with myself

But i'll still stand by my statement that i doubt it is your bridle stretching that has caused the problem.