How we can reproduce it:

Repro Steps:
1. Open the "1 Basics" scene in Samples project provided with the Samples
2. Change the Variant of any point and move the tangent point
3. Note that Variant change does not persist if user were to move the Tangent points

Additional Info:
The workaround is to go into Playmode to make sure the variant is selected to persist.

Found in:
"com.unity.2d.spriteshape: 2.1.0-preview.6"