[Rainrider]

Try changing

CombatFeedback_Initialize(self, text, 30)

to

CombatFeedback_Initialize(TargetFrame, text, 30)

If this causes taint issues you could just try this instead:

local text = TargetFrame:CreateFontString(nil, "OVERLAY", "NumberFontNormalHuge")
text:SetPoint("CENTER", TargetFrame, "TOPLEFT", 73, -42)
text:Hide()

local f = CreateFrame("Frame", nil, TargetFrame)
f:RegisterUnitEvent("UNIT_COMBAT", "target")

CombatFeedback_Initialize(f, text, 30)

f:SetScript("OnEvent", function(self, event, unit, ...)
     CombatFeedback_OnCombatEvent(self, ...)
end)
f:SetScript("OnUpdate", function(self, elapsed)
     CombatFeedback_OnUpdate(self, elapsed)
end)