The entity_lookup plugin should preserve the source order

The Destination field is not guaranteed to store the entities found in the same order as the destination lists them.

For example, Suppose the source has a Category term reference field with term names of Product, Foo, Foo-blue stored in that order. Passing the term names to the entity_lookup plugin will cause the destination entity created to have the destination field stored in this order: Foo, Foo blue, Product

This is because for multiple values, a single query with "IN" is used for multiple values in EntityLookup->query method. The results of an 'in' set, will have whatever the ordering of the index used to look them up. Generally alphabetical / numeric ascending.

Order of entities in the fields is important for a lot of reasons. E.g., matching the taxonomy hierarchy, ordering related posts by most relative, ordering paragraphs correctly, and the like.

The fix for this is to perform individual queries to find the values and then aggregate them in the proper order.

Patch attached in the next comment.