Einstein was a little surprised in 1911 when he discovered that the gravity fields in space could control the local speed of light through them. It was after this that he started talking about the “ether” qualities of gravity fields.

Although he called space “empty” in his 1905 theory, in the 1952 appendix to his 1916 book he said:

”There is no such thing as an empty space, i.e. a space without field.”

By then he knew that the gravity fields of space have some influence on the local speed of light.

There is quite a big difference between his “empty space” opinion of his 1905 theory and his “no empty space” opinion of 1952. He had learned a lot during those 47 years.