Consistent Dive in B-ROR at the same time for different beans

Im pretty new to roasting on the bullet, still trying to figure things out. One question I have is about a very consistent dip I’m seeing in B-ROR at around the 5:45-6:00 mark on pretty much every roast. This happens very consistently- everything seems to be cruising along just fine, then the B-ROR takes a big dip, followed by a sharp spike. I’m not sure what to think of this and/or what to do about it. Example included