Subsonic 5.3 is the last version licensed GPLv3. As of 6.0 it is proprietary. Your port still incorrectly lists LICENSE=GPLv3 for 6.0
https://github.com/sindremehus/subsonic/issues/1 (Repo is for 5.3)
Sorry for the delay handling this. This maintainnership is carried out on a very low priority.
Sent a patch for review:
A commit references this bug:
Date: Wed Jul 26 20:18:21 UTC 2017
New revision: 446695
Subsonic 6.0beta1 was still GPL and then changed to "something".
Submitted by: Allison Nicole Reid <root at cooltrainer org>
Approved by: adamw (Phabricator), jpaetzel (IRC)
Differential Revision: https://reviews.freebsd.org/D11444