By default Expiration Reminder doesn't send notifications after an item has expired. It will send one last notification the day after the expiration date.
You can turn on notifications after the expiration date at the category level.
Sending notifications after the expiration date
To enable sending notifications after the expiration date, first click on Your Account on the top menu and then on Settings.
Then click on Categories on the left menu.
Then click on any category from the list to edit it.
In the edit screen, click on the Category tab and scroll down until you find the Send alerts after expiration section. Turn this option to Yes and enter the following details:
Every: this indicates how often or how spaced apart notifications will be sent. In the screenshot below, they will be sent every 7 days (every week).
Indicate how many after expiration alerts to send: this indicates how many to send. In the screenshot below, a total of 12 notifications will sent meaning 12 notifications every 7 days which will be one notification per week for 3 months. Keep in mind this value can't be larger than 99.
Then click Save.