Running smoker with grill grates at lower temp

Had something happen really strange Sunday on my 640. I had grilled hamburgers and steaks a couple nights before and decided to smoke ribs (St Louis) I had my grill grates installed across entire pit. Instead of changing back to the regular grid I left them in. Was using top shelf anyway. The other thing I did was rotate my chimney about 40% pointing out. I have smoker under a porch cover and with the chimney straight up it was starting to leave soot mark on top.
Long story short I had an off cook. Normally never have trouble with ribs and always cook at 275. Had a hard time getting them done, they were tougher than usual, pit didn't even seem as hot. (Didn't verify with external). Is it possible leaving those grates on somehow threw off the pit, or the adjusting of the chimney? Just looking for answers. Thanks!!
Long story short I had an off cook. Normally never have trouble with ribs and always cook at 275. Had a hard time getting them done, they were tougher than usual, pit didn't even seem as hot. (Didn't verify with external). Is it possible leaving those grates on somehow threw off the pit, or the adjusting of the chimney? Just looking for answers. Thanks!!