This can happen when there is no title code inside your theme. You can add a title to the theme by following the directions below.
Add a title to your theme
View your website
Right click and select ‘View Page Source’
Type Control+F (Command+F on a Mac) to open the search box
Search for
in the file to find the different titles in your theme
If zero results appear then view your themes in Shopify
Select ‘Actions’ and ‘Edit code’ for your live theme
Open the theme.liquid file
Add the following piece of code between the tags
We always recommend you make a backup of your active theme before making any code changes.
##{{ page_title }} | ##{{ shop.name }} {% if template == '404' %}404 Error{% endif %}