Transient is never set. Why?

In one page, I try to set/get two transients. The second works fine. The first doesn't work at all. I can not figure out why.

Here's the relevant code.

    $lat = round($toReturn[location][coords][latitude]);
    $long = round($toReturn[location][coords][longitude]);
    
    $nearbyLocations = [function that gets nearby locations];

    $args = array(
        post_type         = any,
        posts_per_page    = -1,
    );
    
    $mq[relation] = OR;

    foreach($nearbyLocations as $nl) {
        $mq[] = array(
            'key'       = 'location',
            'value'     = ''.$nl[post_id].'',
            'compare'   = 'LIKE'
        );
    }
    $args[meta_query] = $mq;
    
    $transient_identifier = nearme_sites_.$lat._.$long;
    
    if ( false === ( $impact_query = get_transient( $transient_identifier ) ) ) {
        //This transient is never set
        $impact_query = new WP_Query( $args );
        set_transient( $transient_identifier, $impact_query, 12 * HOUR_IN_SECONDS );
    }

    //I do something with the result of $impact_query
    
    $nearbyLocations = [Function that gets nearby locations of a type]
    
    $args = array(
        post_type         = place,
        posts_per_page    = -1,
        orderby           = post_title,
        order             = ASC,
        post__in          = array_column($nearbyLocations, 'post_id')
    );

    $transient_identifier = nearme_place_.$lat._.$long;
    if ( false === ( $impact_query = get_transient( $transient_identifier ) ) ) {
        //This transient is set, as expected
        $impact_query = new WP_Query( $args );
        set_transient( $transient_identifier, $impact_query, 24 * HOUR_IN_SECONDS );
    }

For a fixed lat/long, the first transient is never set, the second is set as expected.

Any thoughts as to why?

Update: it seems that if I do not include a meta_query in my arguments, the transient does work. So, it's not possible to use a transient when the arguments includes a meta_query?