Reposting this comment from curse
Having same issue and thanks for making this great add-on so far !!! Happy
"Moodan 

Posted 1 day ago#17

So far Luna has been working quite well, but there's this one thing that's been bothering me. The health bars in the party frames have like a 0.5 sec delay between the heal landing and the frame displaying the new health value."

Having this same issue here.. Sometimes it seems right sometimes delayed..tested with different amounts of health lost, etc, same thing with health bar after heal landing bar doesn't move for .5 seconds or so.. Server ping is about 40 ms.
Seems to happen less with incoming heal display disabled, but not really sure... Otherwise great so far

From the the next version on i will be using https://www.wowace.com/projects/libhealcomm-4-0/ for heal predictions so all questions regarding this topic should go there.

This is something I noticed with the default blizz ui as well. I think it due to the "generous" 400ms spell batching window.

Yes and because of that i think this will be impossible to fix.