This struck me as odd and it is the first time I have encountered this. Here is my process and the observation. While heating the strike water I occasionally stir the water to get the super hot stuff mixed throughout to achieve a more uniform temp. At 144 F I stirred the water. When the temp reached 158 F I killed the flame and stirred for a minute and the water reached 159 F. Added my grains and mashed in at 152 F (room temp = 58). I put the kettle lid on and covered with blankets. The mash dropped to 151 F 3 minutes in. At 16 minutes in it dropped to 149 F. After 40 minutes I noticed the temp had increased to 150 F (room = 62). At 45 minutes it was at 151. 154 F at 51 minutes (removed blankets, room temp = 77 F). At 56 minutes the temp was 160 F (Removed lid). I was prepping stuff for the boil and ended up letting the mash go an extra 10 minutes. Ending mash temp = 170 F. WTH would cause this? I BIAB, so I don't "flame-on" to maintain mash temp.