net-mgmt/icingaweb2 seems to be dependend on databases/pecl-memcached when build via poudriere and databases/pecl-memcached is somehow supposed to be suddenly broken with FreeBSD port's standard/default lang/php5.6, so the port can't be built anymore via poudriere. This is not very funny, since we need to deploy the package on CURRENT systems. Installing the package via the (personally) preferred but for many-hosts-to-maintain-ineffective way via portmaster/make does not reveal this dependency and builds.
Fixed in r434416.