Fix Signature Gravity Forms field

functions.php

<?php
add_filter( 'gform_get_form_filter', 'my_fix_gform_signature_field', 99, 2 );
function my_fix_gform_signature_field( $form_string, $form ) {
	$replacements = array(
		"~<canvas id='input_\d+_~"         => "<canvas id='input_" . $form['id'] . "_",
		"~id='input_\d+_(\d+)_Container'~" => "id='input_" . $form['id'] . "_$1_Container'",
	);

	foreach ( $replacements as $find => $replace ) {
		$form_string = preg_replace( $find, $replace, $form_string );
	}

	return $form_string;
}