Did you solve the problem with NAT64 internet sharing?
I'd configured it as described, connected my iPhone to newly created network but nor the my app nor Safari/Chrome can't open any URL…
in Console.app i see a lots of 'NSURLSessionTask finished with error - code: -1001' (timeout) errors.
on Mac the internet connection working well, iPhone got an IPv6 adresses and router address is a Mac's one, but iPhone can't communicate at all…
UPD: if i just switching off the checkmark 'Create NAT64 Network' - the internet on iPhone (via Mac's shared wifi network) become working.
UPD2:
macOS version 10.12.4 (16E195)
iOS version 10.3.1 (14E304)
checked on several different iPhones with same iOS version. same issue.