Cache issue?

$query = new WP_User_Query([

            'meta_query' => [

                [

                    'key' => 'ISP_ACCESS_LINK',

                    'value' => '',

                    'compare' => '=',

                ],

            ],

        ]);

In a plugin I have this above query.

This query gets called in the body of a WP endpoint by an external cronjob.

So, to summarize: a remote website, every 10 minutes calls a WP endpoint where I have this query.

Problem is it looks like results are “cached”: I suppose this because after the call, the key ISP_ACCESS_LINK has for sure a value different from the empty string (I verified at the database level).

The strange thing is the value inside is always different than before, but the query reacts like there’s always empty string in the meta.

Could it be a cache issue?