PHP Warning: preg_match() expects parameter 2 to be string, array given in wp-includes/class-simplepie.php on line 2620

Question

The server keeps returning these errors:

[Mon Jan 25 13:38:14.133045 2021] [php7:warn] [pid 18879] [client 13.66.139.39:26051] PHP Warning: preg_match() expects parameter