Kaiser, keep in mind that the coldest spot is at the end of the heat exchanger, which can be significantly colder than your and not having antifreeze in there can cause ice to slowly form on the inside of the pipe, obstructing the lumen, even at 30+ temps leaving the heatpump. Contributing to this might be that your delta T in first stage indicates that you do not have much flow. Based on your data it approaches 10F in second stage, indicating that you only have 4.5-5 gpm. What circulation pump do you have? Model? So your alert might be real, if you have half the flow and no antifreeze. In your climate you might not need much, maybe 10-12% glycol would do it. I would not worry too much about your loop configuration, unless one loop aid air locked. Your flow is off, but your temp of your loop is fine. Even without a reverse return header the additional pressure drop of 30' of pipe each way will not cause more than 10% velocity difference within the pipe, really insignificant for its performance. Plus, you are getting 48F water in, your loop is fine capacity wise.. It is just the flow which is off.