IPv6 can certainly cause some unexpected results in Linux land. Disabling is super easy, depending on your preference of all interfaces or a specific interface:

Create a file /etc/sysctl.d/disableipv6.conf:

For all interfaces:

net.ipv6.conf.all.disable_ipv6 = 1

For an individual interface:

net.ipv6.conf.eth0.disable_ipv6 = 1

Rename eth0 to whatever interface you would like to disable.

Restart after to apply:

shutdown -r now