The NIC mac-address usually doesn’t change (it can be change but there is really no need)
This can cause issues - the network is extremely sensitive to errors in DNS
No - the only thing which can cause interference is the system time
IPv6 can cause dysfunctional network - so unless you have very specific requirements - I suggest you disable IPv6 - IPv6 - ArchWiki
Edit the grub defaults file (install the package micro if you don’t have it)
sudo micro /etc/default/grub
Add ipv6.disable=1 to default cmdline
GRUB_CMDLINE_LINUX_DEFAULT="... ipv6.disable=1 ..."
Hit Ctrls to save and Ctrlq to exit and rebuild
sudo grub-mkconfig -o /boot/grub/grub.cfg
Edit the hosts file and comment the line on IPv6 linke below
sudo micro /etc/hosts
#::1 localhost ip6-localhost ip6-loopback
#ff02::1 ip6-allnodes
#ff02::2 ip6-allrouters
Hit Ctrls to save and Ctrlq to exit and rebuild
Reboot your system and recheck
Also you shouldn’t have to blacklist r8169 - the kernel driver has been good for a very long time