Armour Break / Anvil's Weight not working with Slams

I've just reached Act 4 and wanted to try out Armour breaking with Sunder.
I've taken Anvil's Weight from the Warbringer Ascendancy and taken all the bonuses to breaking armour that I can get to so far. However, whenever I hit anything, I'm not breaking a single point of armour. No partial break, no sunder armour debuff, nothing. I've tried unspecing out of all Ascendancy skills and socketing Armour Break 3 into both Sunder and Leap Slam, neither are breaking armour. I made a new Armour Break skill gem and tried hitting something with that, which did break armour.
I know Anvil's Weight was working earlier because I've been using it for most of the campaign with my Shock Totems, and that mechanic works. I even tested with other Strike skills and it works as intended, just not with any slam skills besides Shock Totem.