It happens. This is when all of the collagen is breaking down, and releasing a lot of liquid, and that can make the temp go down. At this point I usually foil a flat, with 1/4 cup of beef broth, then start probing at about 190*. Good luck!
2 OTG One red one black
22 1/2" black Bar-B-Kettle with rotisserie ring
Brinkman dual zone charcoal grill
Webber Silver Genises B
3 burner camp stove