I'm sorry your question has sat without an answer for so long! Were you able to make progress? I'm not able to reproduce. Here's a test form I used to try out this concept: https://docs.google.com/spreadsheets/d/1CVq1KFMUy4j0OESeORqGKEds1hPRFZ9Z70byLkU5qM8/
I would recommend using selected instead of contains for the reasons described in this thread but I also tried contains and that worked as expected.
The trigger column expression isn't required in this case because your calculation is hidden. It's only needed to do a dynamic default that a user could edit. But again, it shouldn't be an issue and I've confirmed that it works for me with the trigger expression.
I think you're going to need to share more about your form and your Entity List if you're still stuck on this. Are you submitting with Collect or Enketo?