That is weird. I just tried the exact same query with a board in my account and it worked well.
Possible issues I can think of:
Using a wrong board ID
Using a wrong column ID
Looking for values that are not present in the board
Can you please send an email to appsupport@monday.com with the query, response and a screen recording or a screenshot of the board you are using? Our technical team can take a look at it and let you know how to proceed.