All sites in a site collection automatically redirect output to a default page in site

Question

Steps to replicate the problem:

1. Open a SharePoint (2013) list.
2. Select a list item and click the ellipsis (...) and select either Edit Item or View Item to edit/view details of the list item.
3. Instead of showing the right .aspx page, SharePoint is redirecting output to the default page in the site.
4. This behaviour is seen for every list and every site in the site collection.

Does anyone have an idea why this is happening?

Is there a configuration setting for this specific site collection which is causing the problem?

Thank you