Would you mind trying out
my layout (comes with oUF embedded) instead of VuhDo/ElvUI? Some layout/compilation creators tend to do odd things to circumvent certain parts of oUF, of which we are aware of are very bad for performance.
Also, are you showing nameplates with oUF during these drops?
As for possible API issues from Blizzard's end, we are aware of some issues in regards of performance with health events, thus we can't control it.