If it’s pulling antifreeze at all it has prime. Sounds more like a blockage. Is there a screen on the next faucet that might be dirty? Debris got in the suction tube during the switch? Confirm that no other faucets are open, and that the valves are still wide open and the drain one is completely closed, including the two on the waterbay manifold.
I’ve never had an issue switching bottles, even when inadvertently drawing the first one dry, although it might take a bit to get it going again. But pouring several into a large clean bucket, putting a 2X4 under one side of the bucket to tilt it, and clamp the hose to the bucket side so it stays at the bottom of the bucket’s low spot mitigates having to run in and out of the rig watching and changing jugs.
Running hot water taps (at least one) is the most important to protect the most costly to repair device. You don’t need to run a lot of fluid, just so you see it first appear at each faucet. Drain, blow out, or cycle fluid to the fridge ice maker, pump to the toilet, and pour a cup or two in any washing machine drum and run a spin cycle.
I wouldn’t think a few hours outside temp slightly below freezing would be a problem inside a closed up coach. You could leave the HydroHot on set at 40-45 for some surety.
Joel