What is the folder structure for all sites? What types of WordPress installations are each site? Single/Standard, Network/Multisite, Giving WordPress its Own Directory (GWIOD)? Is your subdomain site setup correctly? A subdomain site requires that you create a DNS A record or CNAME record and point the record to the folder where you installed the subdomain site. If the site is actually a subdirectory installation and not a subdomain site then you do not need to make DNS Changes. What is the URL structure? Please explain exactly what this means and what is in the file – “And static HTML file in sub domain to eliminate any WordPress specific redirection issue”.
Examples:
/public_html/ – site is installed in the root folder
/public_html/SiteA/ – SiteA is installed in the SiteA folder – SiteA could be either a subdirectory site or a subdomain site.
URL Examples:
example.com
subdomain.example.com
example.com/subdirectory