"IPv6 was designed to run alongside IPv4 from the beginning. "
Sure, so well that DHCP was an afterthought - the RCF came only in 2003, five years later, - because they thought routers could assign addresses but didn't think about every other need DNS, dynamic IP-hostnames assignment, etc. etc. IPv6 was designed too early and wasn't thereby designed truly for actual needs.
So you got AFAIK, three different ways to have addresses assigned and have to ensure they are configured correctly, then you need the software updated to manage them all.