The reason you should check the WWW part of the url is that it was, at one time, an identifier to let people and browsers know they were connecting to a website server. This differentiated a website server from others, such as FTP or Mail. On websites, they all use the HTTP protocol, so it’s not necessary these days to use the WWW in a URL. Most browsers will automatically assume they are connecting to a web server with just the HTTP designator, or even without it altogether. However, there can be an issue if someone types WWW as the designator in front of a domain name.
Most websites are contained within a PUBLIC.HTML folder on your server. However, because some people still use the WWW designator (sometimes both WWW and HTTP - such as in your URL), web hosts will usually create a redirect link that will direct web browsers to the site within the PUBLIC.HTML folder. If that redirect link is missing, or hasn’t been created by your web host, the link to your website may fail.
This could be the reason why some browsers work and some don’t. Some browsers may simply ignore the WWW bit, whilst other may use it and leave the web server to do a redirect . it’s almost like its being treated as a subdomain of your site.
In the screenshot below, you will see that the redirect link appear in the cPanel of the web host. It simply points to the main site in the PUBLIC.HTML folder. If that WWW link isn’t showing on your hosting, it may well explain why some people cannot access your site via a WWW designator. The simple answer to ensure consistency, certainly when creating URL links within your website, is to drop the WWW bit altogether. It isn’t necessary at all.
To better understand this. Just think what happens if you create a subdomain on your website named “shopping”. The URL for your subdomain would be “shopping.yoursite.com” Your domain name is essentially a subdomain of the top level domain “.com” . whereas, the word “shopping” is is a subdomain of your main domain. These elements are separated by a “.”. Therefore, if a URL is structured as “http://www.yourdomain.com”, the www bit may be viewed as a subdomain. If the subdomain doesn’t exist, then there will be no redirect - a page not found error.