I'm not sure if it's meant to do this or if it's a bug.

There's a task for the Sweet Blossom Orchard that requires killing a rogue necromancer who is 4 stars (Elite). However, when you kill him, the Fortune Event Task Log counts it as a standard kill, not killing a Named/Elite.

The SBO 'elites' don't seem to count. Each spot has a chance to spawn a non-named (not the white raven lady, Damien the Hunter, or Koralai), which will not count towards the task log. Edit: I checked again and apparently those are just Superiors, not Elites. Sorry. The Necromancer might not count because it's a task-triggered thing and won't spawn otherwise, and it doesn't have an actual specific spawn square.
Question, were you using a level 59 team when you fought it?

Yes, my team is level 59 and triggers everything else correctly (including Damian the Hunter, etc.) for the event.

I don't know if this will help, but screenshots of a fight with the Rogue Necromancer & my Event Task Log before the end of the fight and after the fight (you can see that it counts as a kill, but not as a Named/Elite).

Named/Elites are intended to be the static spawns on the maps. Quest/Task related enemies won't count towards progress of that task.