The fermented feed will raise the protein by about 3% of common feed mixes being fermented. The LABS in the ff make all the nutrients easier available for the chicks guts to absorb. All the nutes rise a bit in percentages. I have a chart that breaks down the slight increases based on time fermented but its limited on specific brands of feed used. Most is individual grain based info. FF is nice for being able to dilute the feed with a good grain too and not suffer any major protein/other nute drops when mixed dry.
The FF with what looks like mold should be fine. A film often gathers on tip of a good ferment that hasn't been stirred also as well as sides of container with food that may have been stuck on the side.
It almost looks like a lil spider web or cocoon of a larva in that one spot.
I would wipe that part out and give it a good stir. Add a scoop of dry feed to feed the ferment. I would still feed as ling as it didn't smell rotton (rancid meat smell is bad). It should smell like dough, sour dough-ish a lil sweet.
As far as the flip death. I haven't seen it. I have read about it. But haven't had any friends deal with it either. Seems fully caged, 24/hr feed causes issues like this. You have a different husbandry that allows them to grow nicely on good nutritious food and move around, I think you'll be ok there. What I have read is overfeeding and no room to move causes these issues...none here yet and I don't think you will either
I think you are great on the losses too! Seemed like the 1st week was always the hardest for them and that when I list mine most often. They make it past that and are thriving you're golden! I have already stepped on 2 and tripped and landed on one as well as shut one in the door on accident...all are ok! But if they start dying its probably my fault for squishing a determined dinosaur lol