If you have 2 classes (class1, class2) with the same attribute identifier (attr1), and run a search for attr1 Criterion\Operator::CONTAINS array("some_value"), then in legacy search it will work as expected.
But in solr search the query ends up looking like class1_attr1="some_value" AND class2_attr1="some_value" so nothing gets returned.

PR: https://github.com/ezsystems/ezplatform-solr-search-engine/pull/154