The def/burn is growing up the stem, please help!

Okay so they're in week 5 of flower, but they've been in veg for 9 weeks and I've been feeding it bioflores with guano big bud in ffof, I know they're just flowering so some leaves should fall off but it's setting to get a lot

Looks like its just shedding old leaves. What does the new growth look like?

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New growth looks fine, definitely a lighter green than when it was I. Vegetative mode but not yellowing at all

I'll post a pic tonight when I get home