IPv6 config rule expands to no valid combination ?
Seriously, did I really get such an answer as shown below? :-\
Dude, you do NOT 1:1 NAT IPv6 like this. WTF. There's NPt for IPv6.
P.S. Filed a bug: https://redmine.pfsense.org/issues/4536
(Note @OP: Fixing that bug will prevent you from configuring similar BS. Meanwhile, kindly remove that nonsense yourself.)