PDF attach to emails not saving selection

Hi,
I am having an issue with the ‘Attach the PDF to the following WooCommerce emails’. My PDF is created when the order is ‘processing’ and then it is meant to send the PDF in the ‘New Order’ email.
I select ‘New Order’ from the drop-down menu then closed the template settings box. I then save the invoice file. I then leave the editor page back to dashboard. After this is test my orders and the PDF is not attached.
I then take a look back at the invoice editing page and the ‘New Order’ is no longer saved in the ‘Attach the PDF to the following WooCommerce emails’ box. I have done this multiple times using the web browsers of Chrome, Firefox and Edge.
I had this working with no issues for over a year, I made no edits in the template and it has suddenly stopped saving the ‘new order’ in the attach in email box.
I also noticed when I first went into the invoice template to investigate why the PDF’s weren’t sending, my Delivery Address information had changed its alignment from left to middle. I have changed it back and saved it successfully without it reverting to middle alignment, but I just thought I might mention it as these problems could be related to an update or something.
Thank you very much for any help in advance.