I've never done this, so asterisks as appropriate, but if you're using IPv6 to assign addresses from your block internally (that is, you aren't NATting your devices behind the router), you now have to invalidate all of them.

With IPv6, your ISP gives you a block of IP addresses which your router then divvies up among its clients. Each device on your network has a unique public IPv6 address, rather than sharing one and your router using NAT and port forwarding to direct traffic.

This makes dynamic DNS much more complicated because you can't just update the AAAA record with the address of your router, you need to update records for all clients that need to be externally accessible.

This is not an unsolvable problem, but it does make things a bit more complicated than just punching your DynDNS credentials into your router config or running Namecheap's DNS tool on one of your machines.