WowAce

Looks like alpha resolved to > 1 in this scenario and as of 10.0.0 they're not auto-clamping into the 0-1 range anymore.

Patch 10.0.0 (2022-10-25): Now throws an error when the alpha argument is outside the [0, 1] range.

929x Interface/AddOns/Omen/Omen.lua:985: bad argument #1 to 'SetAlpha' (Usage: self:SetAlpha(alpha))
[string "=[C]"]: in function `SetAlpha'
[string "@Interface/AddOns/Omen/Omen.lua"]:985: in function <Interface/AddOns/Omen/Omen.lua:978>

Locals:
(*temporary) = OmenFlashFrame {
0 = <userdata>
elapsed = 0.744000
texture = Texture {
}
}
(*temporary) = -0.003333

Reposting from the original 10.0.0 issue...

I was able to fix this by updating the function at 975 with the following:

		flasher:SetScript("OnUpdate", function(self, elapsed)
			local totalElapsed = self.elapsed + elapsed
			if totalElapsed < 2.6 then
				local alpha = totalElapsed % 1.3
				if alpha < 0.15 then
					self:SetAlpha(math.min(alpha / 0.15, 1))
				elseif alpha < 0.9 then
					self:SetAlpha(math.max(1 - (alpha - 0.15) / 0.6, 0))
				else
					self:SetAlpha(0)
				end
			else
				self:Hide()
			end
			self.elapsed = totalElapsed
		end)

There also seemed to be an issue with using "local elapsed" where it wasn't actually increasing the self.elapsed property properly. Changing the var name to not conflict with the callback parameter name seemed to correct this issue.