Basically title, if you use both Hypothermia (1 pt) and Incineration (only tested 6 charge attack) shatter strike is doing double the damage. Basically Incineration is doubling up with this. I didn’t test Exothermic + Flame Reave but I’d expect it’s the same. I had incineration + illuminating fire + hypothermia with 6 charges and prereqs (9 total points)
No screenshots, but max crit I saw jumped from 14k to 26k with one point in hypothermia and rest of the firebrand tree unchanged (possibly 11 charge release vs the 5 expected)
Edit: quick confirmation, it appears to double count in some way, if I attack twice (2 listed charges) with Firebrand then use Shatter Strike, it still has a guaranteed crit, basically meaning it’s counting as either 3 or 4 stacks. Also confirmed the same behavior with Flame Reave and the charge using firebrand ignite node