The FreeBSD port builds acme-client with the static versions of the libressl libraries when libressl is not the default ssl. This worked until the libressl port was upgraded to 2.7.2. If you run:
acme-client -bmnNe -vvv -F -C /tmp example.net example.net
you'll see:
acme-client: tls_init: No error: 0
Here's a link to the FreeBSD PR:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=228438
As far as I can tell the issue only surfaces when using the static libraries.