Hi,
Thanks for the access.
I check your website and everything is perfect and it's totally logical that no email is sent to the customer.
why the customers are no longer receiving email
I guess that it never be the case except if you modified the HikaShop core.
There is no "login" step in your checkout so, there is no email attached to the order, just an IP.
If you check the "customer" section in an order, you would not see any information about the customer.
HikaShop can't find any email so it can't send an email to this customer.
You have a "no registration" but HikaShop can create virtual users for storing emails and storing some information (like the address, etc).
Just have to add the "login" step in your checkout workflow.
You have a custom field for the email but HikaShop can't know that it has to use this field to send an email.
So, except if you modified the HikaShop core before (that you had/will loose with updates), I am sure that, in this current configuration, it can't work.
Regards,