I ran my first batch and the alcohol was reading about 94%. Tested it again the next day and it dropped to 70%. I can't see how this is possible. Is it?

Warm liquids have a lower density then cold, or in other words it has less buoyancy. Your instrument sinks lower in the warm alcohol/water mixture and makes it look like it is a higher proof. When it cools it looks like your proof has dropped.

As an experiment go ahead and put a sample in the freezer for a few hours and then measure it. You will be surprised at the change.

The instrument should have come with a temperature correction chart. Either use it or only measure your sample around the recomended temperature ,which tends to be 20C,.