I've had similar happen to me before. In my case it was because the bigger and denser buds got mold due to high humidity, which caused the stem inside the bud to rot and stop pulling water to the top of the plant. If I were you i'd check to see if the same has happened to you, probably near the bottom of where the branch is drying up you may see some rotting on the branch/bud.
Luckily it seems pretty isolated to that one plant though, so it is odd. Maybe it collected some water at some point?