Balance Of terror is not working

Hi, I was testing the new gem balance of terror modifier with the mod "gain +#% of physical damage as extra random element if you've cast elemental weakness in the past 10 seconds" but it doesn't work
video:

The random element is determined per attack/cast, so it doesn't display on the character sheet beforehand.

Go try killing some monsters while the buff is up, and seeing if any shatter from your crits--since your EK only has physical/fire damage normally, those would be casts where the random element was cold.