I usually leave adding salt as late as possible in mixing/kneading.
When it is added I can see (in my mixer) the considerable degree to
which it tightens dough, but it will also inhibit further development
of gluten (so therefore add late).

Nobody seems to have listed or questioned the hydration of this rogue
batch of dough? Too much water for the flour mix in question is surely
the most likely explanation for its sloppiness. Even a one percent
change either way can make a break a given mix. Aside from this
leaving it to proof for too long (if it was in any case borderline in
terms of the hydration the mix could take) could undoubtedly allowed
acidity to develop to the extent that gluten strands were eaten/broken
away - and the absence of salt could have contributed to this.

Maybe you didn't change your hydration but did change your flour brand
or mix? A change of flour brand could easily result in a 5% difference
in water to be used to achieve the same consistency dough, even
between white flour brands both purporting to be 'strong'.

I know its not the case here, but I find any addition of rye, even a
very small one, to mix can both speed up dough maturation and increase
risk of dough going sloppy very considerably and I normally adjust for
this by considerably reducing hydration compared to a non-rye mix

yours
atty