Smartlist fails with "Not Was Sent Email" filter that uses a "contains" constraint
Hi community,
I get a strange error when using a smart list filter "Not Was Sent Email" with a "contains" constraint: No matter what I enter for that constraint, the smart list won't accept it and return
Error running Smart List
Check your Smart List configuration

Has anyone experienced this, too? What's going wrong and how can I solve this?
I've already tried cloning the smart list, and using it in combination with another smartlist that filters for membership in the above smartlist without the "Not Was Sent Email" filter plus adds just that filter as a second step.
Thanks!