Simple Product Options for WooCommerce By Pektsekye

Plugin URL: https://wordpress.org/plugins/product-options-for-woocommerce/ Solution: https://wordpress.org/support/topic/compatibility-with-fox-woocommerce-currency-switcher-professional-2

open file wp-content\plugins\product-options-for-woocommerce\Model\Observer.php
find function add_option_price_on_checkout($cart)

on the same top place next code:

global $WOOCS;
$backup_filters = null;
if (isset($WOOCS) AND $WOOCS->is_multiple_allowed) {
        $backup_filters = isset($GLOBALS['wp_filter']['woocommerce_product_get_price']) ? $GLOBALS['wp_filter']['woocommerce_product_get_price'] : null;
        unset($GLOBALS['wp_filter']['woocommerce_product_get_price']);
}

on the same bottom, before code WC()->cart->set_session(); place next code:

if ($backup_filters !== null) {
        $GLOBALS['wp_filter']['woocommerce_product_get_price'] = $backup_filters;
}

Shortcodes, functions, actions and filters reference for FOX WooCommerce Currency Switcher