[This is not a bug in the port per se, apologies if I am not reporting it in the right place.]
devel/hs-git-annex is not available from the pkg repositories anymore (both latest and quarterly, at least for amd64), but https://www.freshports.org/devel/hs-git-annex/ does not list any problem with the port. Unfortunately I cannot confirm that the port actually builds, my machine being very limited resource-wise.
git-annex depends on esqueleto package, which doesn't build with current GHC. So, we have to wait for new esqueleto release to make git-annex available.
It looks like esqueleto was removed as a dependency in http://git-annex.branchable.com/news/version_7.20181121/.
It has and building git annex with stack is possible if you use the system GHC (their prepackaged GHC isn't ino64 compatible).