It’s been bugged since 11.1 — use the macro below and it’ll work somewhat more consistently.
Essentially, divine toll’s radius for holy shocks after the initial target is only 5 yards. IE. If you cast divine toll on yourself and only have 2 raid or party members within 5 yards, you’ll only receive 3 holy power.
This macro makes it cast on no one in particular, bypassing the bug and casting it on anyone within 35 yards, as intended.
The bug also only happens when using divine toll for healing. It works fine if you use it offensively.
#showtooltip
/cast [@none] Divine Toll