Could you tell us what 4xx error you are getting exactly?
This class of status code is intended for situations in which the error seems to have been caused by the client. User agents should display any included entity to the user.
Please note that usually the root of the URL is accessible and it will be redirected to default page of your application.
Also, sometimes certificate negotiations may be required and upon failure server may throw 403 (forbidden) or 401 (Unauthorized). It is 404 (Not found) you should concern mostly.
You should look into its header details to find the client IP and the referer (from which previous page user came from) and the User Agent related info.
Another way of doing this is by using a client side recorder application such as Fiddler or Chrome debugger or Mobile App Remote debugger to point out exactly which page is causing this. Also you can have a look at UEM.
In the PurePath Dashlet you can show the "Client IP" column and see which clients send these requests to your server. Normally these kind of requests come from monitoring tools or loadbalancers etc. I would check if the client IP is the same for every request and then try to identify the IP address. Maybe its a known IP address and you can figure out, what component is causing these requests.
Hi Praveena, I believe that 403 (Forbidden) for root is mostly due to handshake failure which is something normal. However, do report this behavior with application team or webmaster. They will be in a position to suggest better.
Also, take a look what @Birtan advises.