In all double stops it is important that both fingers land together.
In 6ths (and 4ths) this can mean that a finger must lift very quickly to be ready on the adjacent string. For instance here the 2nd finger plays in the 1st chord on the E string and then has to move to the A string.
Practice this silently (without the bow) so that you can focus on the finger action.
Tempo and articulation are factors in how high you lift the fingers.
When descending in 6ths it is sometimes possible to just slide fingers across as shown here.
The same principles apply in both major and minor 6ths.