WooCommerce sites that are using multiple currencies can result in a third-party plugin triggering a call to get_cart before the wp_loaded action, which is something explicitly not allowed by WooCommerce.
So far, we have had reports while using oGone payment gateway, WC Deposits & Booster for WooCommerce plugins, but others may be affected too.
We are working on the best way to resolve this and release an update but in the meantime, you can try the workaround below.
Edit the wp-content/plugins/woocommerce-multilingual/classes/multi-currency/payment-gateways/class-wcml-currencies-payment-gateways.php file and change line 30 from:
add_action( 'init', array( $this, 'init_gateways' ) );
add_action( 'wp_loaded', array( $this, 'init_gateways' ) );