Class Field Checkbox and ACF Checkbox bug w/ fix - nested array data

[shanemac10]

FYI - I have the same issue as mentioned here, and did a little digging and it appears the data is double nested in an array when it happens to me. And since you are running the extracting ternary once, it doesn't catch it. I just copy and pasted that ternary (on /wp-user-frontend/includes/fields/class-field-checkbox.php line 183), and it seems to work great now.

Turned this...

    public function render_field_data( $data, $field ) {
        if ( empty( $field['options'] ) || ! is_array( $field['options'] ) ) {
            return;
        }

        $data     = is_array( $data ) ? array_pop( $data ) : $data;
        $data     = explode( '|' , $data );
        $selected = [];

        foreach ( $data as $item ) {

into this...

    public function render_field_data( $data, $field ) {
        if ( empty( $field['options'] ) || ! is_array( $field['options'] ) ) {
            return;
        }

        $data     = is_array( $data ) ? array_pop( $data ) : $data; // <-- added this
        $data     = is_array( $data ) ? array_pop( $data ) : $data;
        $data     = explode( '|' , $data );
        $selected = [];

        foreach ( $data as $item ) {

Ref errors:

Warning: explode() expects parameter 2 to be string, array given in .../public/wp-content/plugins/wp-user-frontend/includes/fields/class-field-checkbox.php on line 185

Warning: Invalid argument supplied for foreach() in .../public/wp-content/plugins/wp-user-frontend/includes/fields/class-field-checkbox.php on line 188