MariaDB: No database selected error on some query [migrated]

I have a php code that rise a query against a MariaDB (using MariaDB 10.5.11 on debian 11) table; I use php-mysql prepared queries for this task as reported in the code below:

if($this->dbcon->begin_transaction() === false) {        $this->errNum = -1;        $this->errText = "Unable to start transaction: " . $this->dbcon->errno . " - " . $this->dbcon->error;        return false;}try {    $query = file_get_contents("recursivelyRemoveShares.sql");   // (1) If replaced with a SELECT works fine!    if($query === false) {        $this->errNum = -1;        $this->errText = "Unable to read query (0)";        return false;    }    $stmt = $this->dbcon->prepare($query);      // Err 1046: No database selected    if($stmt === false) {        $this->errNum = -1;        $this->errText = "Unable to prepare statement: " . $this->dbcon->errno . " - " . $this->dbcon->error;        return false;    }    $stmt->bind_param("s", $uuid);    $stmt->execute();    // Commit transaction    $this->dbcon->commit();} catch (Exception $ex) {    // Rollback transaction if something goes wrong    $this->dbcon->rollback();    $this->errNum = $this->dbcon->errno;    $this->errText = $this->dbcon->error;    return false;}

When running $stmt = $this->dbcon->prepare($query); the database raise an Err 1046: No database selected; however I did some other operations before that executed successfully, using the same DB connection.

This is the query I read with file_get_contents:

DELETE FROM `shares` WHERE `itemuuid` in (  WITH RECURSIVE files_paths (id, parent) AS  (    SELECT uuid, parentuuid      FROM core_data      WHERE uuid = ?    UNION ALL    SELECT e.uuid, e.parentuuid      FROM files_paths AS ep JOIN core_data AS e        ON ep.id = e.parentuuid  )  SELECT id FROM files_paths)

Note that is a recursive CTE query.

If I replace the $query with a SELECT query, all the code runs correctly (no error 1046 raisen).

Any help or idea is appreciated.

Monday Sept 13 edit!!

Same code tested on MySQL 8 works fine! Just removed MariaDB and installed MySQL8, no changes on php codes or SQL queries! Is this a MariaDB issue?