Wireguard: Automatic outbound NAT rules are applied to the WG interface
It's unexpected that they should be there for a site-to-site setup.
Additionally the WG interface subnet is included in the 'tonatsubnets' table so it NAT's it's own traffic:
WG0 icmp 172.27.116.16:7147 (172.27.116.16:53398) -> 172.27.116.1:7147 0:0 2.955 K / 2.955 K 84 KiB / 84 KiB
21.02-DEVELOPMENT (amd64) built on Fri Jan 22 00:08:37 EST 2021 FreeBSD 12.2-STABLE