processing order email subject issue

Hi,
I noticed an issue concerning the subject of processing order email notification. When order status changes from “on hold” to “processing”, the email subject of processing order notification is the same that “on hold” subject. ( “Your sitename order has been received!” instead of “We are working on your order #xxxxxx”).
Deactivating your plugin the processing order email subject is the right one (“We are working on your order #xxxxxx”).
My website runs Woocommerce 3.6.4, Polylang 2.5.4, Hyyan WooCommerce Polylang Integration 1.3.0 with the changes described here https://github.com/hyyan/woo-poly-integration/pull/414/files
Please help, thanks