Is it cmpulsory to enable DNS IPv6 to IPv4 to host IPv6 listner?

Rather than focusing on one client that may or may not have its own broken setup, you need to make sure you get IPv6 on your site working dual-stacked with IPv4. That is, make sure IPv6 works on your site independent of IPv4. Many client machines, particularly mobile devices or those on cable connections, will have IPv6 (and some don't have native IPv4).

That said, it sounds like the client you were focusing on may be seeing a IPv4-mapped IPv6 address, which is likely not what you want. Don't enable the "DNS IPv6 to IPv4" if you don't know what it does. Here is a link explaining that feature https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/dns-services-implementations-12-0-0/9.html