When Dr. Brackett, Gage and DeSoto have their meeting regarding communication, Dr. Brackett states that from then on, the P.M.s will state their squad number when repeating orders from hospital. They never did in any episode after that.
During stationary bike scene at fire house, Kelly's sweat pattern is not consistent.
After Squad 51's last rescue. The next scene shows the squad driving on a road and they turn their Emergency Red lights on, so that they can back the squad up into Station 51. It's very clear that the man driving the squad is not Roy or Johnny, as they don't have mustaches.
When Station 51 gets toned out for the structure fire at the end of the episode the Squad leaves the bay first, as usual. En route the dispatcher redirects the Squad to a different emergency, the man trapped under his car, and we see the Squad is now following the Engine.
At the scene of the car on the roof of the house, Roy tells the boy in the back seat to move to the door and get out. Doing that shifts the center of balance forward, causing the car to begin to rise at the back and nearly falling off the roof, causing Roy to use all the force he has to keep the car level. Roy should have known to tell the boy in the front seat to climb over to the back seat. That would have moved the center of balance toward the back of the car, keeping it from tilting forward.
As Dr. Brackett meets with Roy and Johnny about the communications mix-up, he plays back recordings of Squad 51's conversation with Rampart, and Squad 49's conversation with a pediatric hospital. During the meeting, Dr. Brackett rewinds the Squad 49 tape so Roy and Johnny can hear the "10-4", but when he re-inserts the Squad 51 tape to replay the "10-4" there, he fails to rewind the tape first.