BIP Report LOV becomes read-only when the number of characters increases

Summary:

Content (required):

I am trying to build a report with prompts for Degree, Certifications, Languages, Major etc. profile items. I have used SQL queries as LOV to get the content item values to display. The Major for Degrees content type is configured as a free-text field mapped to text 240_1. If I take the distinct values from that field, all other parameters become read only without a drop-down. See screenshot below.

But if I take a substring of the Major field and restrict it to 20 characters, then it shows properly as expected.

The other prompts that I have in this report have values going up to 50 characters and show up fine in the LOV, only the Major field which is mapped to