Bud rot on lower popcorn buds?

I have a 400w cabinet grow, 7 weeks in flowering with 7 plants in scrog.
Everything looks fine except for the lower tiny buds on one plant where all the pistils have turned brown at the same time, whereas the main cola of the same plant is still mostly all white.
At a quick glance it looks like they (bottom buds) are just ready for harvest but it actually seems like they have all died.
Could this be budrot, if not what else could it be?




Top pistils removed to show brown/dead bud underneath


The main cola from the same plant, far and close up

trim cut off all affected crap

I already removed all the lower buds, they are useless anyway. Whatever it is, so far it had only effected the sites under the canopy where no direct light gets through.
View attachment 1219431

The lower buds where the main cola starts are also looking similar.

Why would the lower, smaller, surrounded by air buds be effected and not the dense buds on top?
Can anybody say for sure that this is budrot?

+rep for help

Bump..I have no idea but I hope somebody can help you..Good luck

Bumping so you can get an answer

thanks nunotmp.
I guess Ill take another closer look at the bottom of the main cola tomorrow to see what the situation is like there. Hope I wont have to end up cutting part of it, its turning into a nice huge bud