Before strongSwan 4.6.0 starter did not use the modular kernel interfaces, thus, when it tried to detect an IPsec stack it failed:
Starting strongSwan 4.5.3 IPsec [starter]…
no netkey IPsec stack detected
no KLIPS IPsec stack detected
no known IPsec stack detected, ignoring!
/usr/local/sbin/ipsec: unknown IPsec command `scepclient’ (`ipsec –help’ for list)
Fortunately, this detection is not really needed on FreeBSD so simply ignore this message.