Yes, actually I just figured it out:
So when I ran this command directly:
reattach-to-user-namespace /Applications/Sublime\ Text.app/Contents/SharedSupport/bin/subl filename
I got this message:
warning: reattach-to-user-namespace: unsupported new OS, trying as if it were 10.6-10.8
warning: _vprocmgr_move_subset_to_user failed
warning: reattach-to-user-namespace: unable to reattach
So I figured reattach-to-user-namespace must be out of date. To fix I did a:
brew uninstall reattach-to-user-namespace
brew install reattach-to-user-namespace
And it started working.
Thanks!