Can you change the multiplier for signature fields and let me know if that changes anything? A higher multiplier will create a clearer signature the default multiplier is 5.
functions.php
add_filter(‘frm_sig_multiplier’, ‘change_sig_multiplier’, 20, 3);
function change_sig_multiplier($multiplier, $field, $value){
if ( $field->id == 171 ) {//Change 171 to the ID of your signature field
$multiplier = 10;
}
return $multiplier;
}