Took a long time testing it now. Frozen dmg seems to be working as it should be but there was a little mistake: The mountain path added 200 extra cold dmg to the player which was meant for the frozen tundra area. This got fixed and now happens in the frozen tundra area instead. So you had more cold dmg in the mountain than in the tundra this could have lead to what you experienced. It is fixed now.
Snow Jaguars attack element is now fire, it accidentally was set to water. The boss now takes dmg as it should be after applying the field effect. The field effect skill now is also learned at level 10 instead of 15 making it less tedious to get. Also Snow Jaguars form also has now "Frozen" immunity.
Thanks a lot for the reports!