You can face with this issue after update. The possible reasons are:
AliExpress supplier changed variation's names and plugin can't update product because the existing names are different from those which were used before.
AliExpress supplier added or deleted some variations/attributes and plugin can't correlate them with the existing ones.
How to resolve:
Reset the product: go to Product Options → Supplier → Reset → Update Product: variations will be reset.
Then go to Update and click Update Product: