I have noticed that when running hot water using a combi, at a reduced
water rate, the water is "very" cloudy. It clears to very clear in a
glass in about a minute. Yet, when the flow is faster the water is
always clear. Does anyone know why this happens?

It is air in the water. It comes down the pipe that way.

On an old style vented cylinder, the water settles in the cylinder and the
air is vented off the top. This effect does not happen with an unvented
system, like a combi or heatbank, so the air makes it all the way out of the
tap. The sudden pressure change as it leaves the taps makes it form bubbles,
as the water can hold less air when heated (which is why the cold doesn't
form bubbles). When running at a high flow rate, the outlet temperature
drops and the pressure change is less, so fewer bubbles form.

Christian.