Empowered Sparks support Gem

Getting some extreme inconsistent behavior with the Empowered sparks support on monk

slotted in to Killing Palm
I'll get the charges
but the "Empowered" attack only seems to happen once, and then only if the next action is a charge spender (falling thunder)

no other quarterstaff attack I have slotted, nor wing blast from talisman seem to get the sparks

Video evidence: https://youtu.be/XWEC2XCXous