I phoned eBay and this is the response I got
Thank you for contacting eBay, we have received your situation where you are reporting an issue related to Not receiving eBay messages regarding sales you make. You may want to check your email preferences on the site and if you see something is enable, try disabling it for 5 minutes, then re-enabling it to refresh the setting in our system. To do this go to the account settings and then click "Communication Preferences" and there's an option that says "Notification Delivery Format", you can click on 'Edit' and disable and re-enable the email preferences there to refresh your email notifications.
I haven't done it so far because I havent had the problem again yet.