If you run both IPv4 and IPv6, make the endpoints independent. One hostname for A-only and one hostname for AAAA-only removes ambiguity and makes debugging much faster.
Minimal rules
1) Keep beacon4 as A-only and beacon6 as
AAAA-only.
2) On the client, pin address family using ip-version.
3) Verify DNS results using dig before blaming the
proxy stack.
dig +short beacon4.example.net A
dig +short beacon4.example.net AAAA
dig +short beacon6.example.net AAAA