In November 2018/12.30 track, you can no longer disable BNF syntax checking as you could in prior releases, see attached Release Notes document regarding that change.
I would suspect it has to do with the [ ]'s around the variable, or potentially the other set by Table is. Hopefully this may help you get things resolved. I am going to move this to the QlikView product forum as well, others may have something else to try as well.
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