So i'm doing this 11 week deadlifting program, my old max was 410 probably 2+ months ago. With crazy back bending..

Like this:
YouTube - 400lb deadlift

So I was on.... week 8 probably, doing 365 5 times, and the 4th and 5th one rounded bad.. The next week was 385 3 times and they all rounded my lower back, week ten (tomorrow) is 400x3x2, then week 11 is 450x1... I don't know if I should do the 400x3. I do heavy goodmornings with good form too.

Now my question is, this must be a weak lower back problem right? Well if I switch to sumo deadlifts could it help?and also could you guys critique my form on the vid

thank you

If I were you I'd drop down in weight until you can stay C backed the whole time. The form on the video was definitely not good.

I have two stress fractures on each side of my 5th lumbar vertebrae, as such, my back is a little weaker than it should be. My physical therapists recommend that I do sumo deadlifts to reduce strain on the back and I tihnk it is, in fact, easier to keep a straight back doing sumo.

Honestly though, I would not continue to deadlift that amount of weight if I could not keep my back straight and do it with good form. Of course, I am much weaker than you, so, take from that what you will.

lower the weight and do it with good form, keep the back straight. It looks like a weak lower back, yes. Sumo has less back in it, but then you will be working around a weakness instead of fixing it.