Post a photo of the stress point, where the leather strap goes over the D ring, that small piece of leather is how strong your collars are, and when it stretches and the D ring can twist and turn around to enlarge the hole more, then it snaps, you'll be left with a leather band with nothing to attach a lead to, which isn't very useful is it?
I'll give you some advice, don't try and make your own gear look better by mugging mine off.
Yes there are a few dogs with gear on that I have made, there's a hard earned reason for that.