How to fix "Warning: Illegal string offset 'echo' in…"

I know this has been asked but the solutions aren’t working for me, or I don’t understand how to implement them. Here is the error I’m getting and it didn’t happen as a result of a PHP update:

Warning: Illegal string offset ‘echo’ in /home/content/66/7404166/html/wp-content/themes/hybrid/library/extensions/custom-field-series.php on line 82

Ad here is the code from around line 82 of that file:

$series = apply_filters( 'custom_field_series', $series );

	if ( $args['echo'] && $series )
		echo $series;

	elseif ( $series )
		return $series;
}

Any tips how to fix? Thanks in advance!