Charged jump only works every second time?

I tried adding a charged jump function into my game, which on short press makes the player jump normally, but when held down makes the player jump higher depending on how much time it was held for.

hum:SetStateEnabled(Enum.HumanoidStateType.Jumping, false);

uis.InputBegan:Connect(function(input, t)
	if t then return end
	if input.UserInputType == Enum.UserInputType.Keyboard then
		local key = input.KeyCode;
		
		if key == Enum.KeyCode.Space and not(shiftdown) and not(inair) then
			if canJump and stamina.Value > 15 then
				spacedown = true;
				print("down")
				while spacedown do
					counter += 0.1;
					wait(0.1);
				end
			elseif stamina.Value > 5 then
				hum.JumpPower = 25;
				hum.Jump = true;
			end
			
		else (...)
		end
	end
end)

uis.InputEnded:Connect(function(input, t)
	if t then return end
	if input.UserInputType == Enum.UserInputType.Keyboard then
		local key = input.KeyCode;
		
		if key == Enum.KeyCode.Space and spacedown then
			hum:SetStateEnabled(Enum.HumanoidStateType.Jumping, true);
			hum.JumpPower = math.clamp(counter*20, 25, 60);
			hum.Jump = true;
			spacedown = false;
			counter = 0;
			inair = true;
			print("up")
		else (...)
		end
	end
end)

hum.StateChanged:Connect(function(old, new)
	if (old == Enum.HumanoidStateType.Freefall) or (new == Enum.HumanoidStateType.Landed) then
		if not(spacedown) then
			hum:SetStateEnabled(Enum.HumanoidStateType.Jumping, false);
			print("landed")
			inair = false;
		end
	end
end)

The player only jumps every second time, and always a small jump, no matter how long I hold it down. There are no errors in the output, and "up" and "down" only appear when the player doesn't jump. Any ideas why it doesn't work?