Originally, General Relativity did not predict if the universe was expanding or not. Einstein could do whatever seemed to be appropriate according to observations. It is only after that Hubble observed a redshift of distant galaxies that Einstein fixed his equations for an expanding universe. At first, he added a mathematical term to his equation to make a static universe. He said that it was his biggest blunder.

Today, with the discovery of Dark Energy, this added mathematical term can be used to explain how Dark Energy behaves, at least approximately. So many physicists think that Einstein's biggest blunder was not a blunder after all. This was just an unknown and it is still an unknown to some extent.

The vacuum energy explanation is possibly just a big blunder. It is in my humble opinion. It is not observed in any way concerning Dark energy.

Vacuum energy is ill-defined in physics. No one knows what it is and how it works exactly. It is a concept used to explain some observations in Quantum theories. In fact it has no true meaning in General Relativity.