Too much starter and/or time?

I made up a couple loaves of Tartine 3 Sprouted Kamut.  In all things it went really grand.  Probably one of the highest hydration doughs to date (85%) that handled stunningly.  Was very pleased and hopeful.

Except I got totally rotten oven spring.

Of course, I changed two things and wondering if that was my undoing.  The recipe called for 150 g levan and I used 250g.  It was combination a typo and then not catching my mistake.  And then due to time constraints, I needed to do an 18 hour retard in the refrigerator after the first couple hours of bulk rising.

Did I possible undermine my gluten structure with the extra acid?

Again, it handled well.  Lot's of tension.  Nice fast (40 minute) proofing.  Slashing was great (damn, the first time I've used a lame, WHY didn't someone tell me how much better they are than razors?).

Thoughts?