When Rollin’ Hot procs from Combustion, it’s supposed to last for 14 seconds.
However, if the 4-set bonus procs on its own and it has more than 7 seconds left, it will munch it and you lose as much as 6 total seconds from it if it doesn’t proc again by the time Combustion ends. Really makes our damage inconsistent on big pulls.
Video proof - https://youtu.be/khIncEYPX2E