Dark brown leaves

From the look of your weeks pictures that single plant needs a closer inspection because it looks like the rest are unnafected. take it out of the tent so you don't spread any mould spores and inspect it thoroughly for mould. Like others have stated I would also harvest that top at the very least but take it out of the tent before you do anything to avoid any contamination that could take hold during the drying process.

crispy? the leaves are dying they are already yellow and at the end of their lifecycle so it may be natural death. one other possibility is budrot. when there is budrot inside the leaves protruding from rotten buds can turn crispy brown. hope its not that tho. i personally would harvest that particular top 1 week early and inspect it just to be on the safe side.