I have no issue using the Heart of Azeroth necklace and its Crucible of Flame essence. Here is a quick video of my Mage doing the heals just a few minutes ago.
link: https://www.wowhead.com/azerite-essence/the-crucible-of-flame-12
What I am clicking is a macro for the Crucible of Flame’s Concentrated Flame ability that I keep around just to do quick heals on friends or mobs.
#showtooltip
/cast [mod:alt,@player] [] Concentrated Flame