FWIW, note also that the

    return "SOMETHING";
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statement in the OPed code is unreachable.

Yes - I should have pointed out the reason for that line in the question...
It was added as part of trying to work out what was actually happening. Having a definite return ensured that I was not getting a return value from the last evaluated expression. I did try to eliminate some of the possibilities before turning to the Monastery.