Seing as you lost all your charge I would be inclined to say you have a leak somewhere. As long as you test both the LP and Hp Sides of the system it should be a fairly obvious drop, sometimes a small leak can hold pressure ok but then fails a vac drop test straight away.
Your original problem was lack of charge, once re-gased everything worked fine which shows your compresser was doing its job ok. The gas has leaked out somewhere, whether that was a small leak over time, or a larger one which ditched the whole charge in short period of time only a good press/vac test will tell.