Hi,
Which BO front-end tool are you using to consume the BEx query?
It's important to know because the different BO front-end tools support different metadata and functionality. E.g. DesignStudio does not support "mandatory" variables according to the document(slide 32) which I shared yesterday with you.
Did you try to regenerate the BEx query using t/code RSRT?
Just to be sure, sometimes it helps.
Best regards,
Sander