The permissions on /var/lib/tor/SERVICE_NAME/ are "rwx--S---" and it's owned by debian-tor, which worked for 0.2.9.10.
What user is your tor process running as?
The Ubuntu packages from d.t.o run Tor as "debian-tor". I would expect 0.3.0.7 to do the same, but it dies immediately, so I'm not sure.
There should be a log line with the user name in it.
Or you could use something like ps.
Otherwise, you will need to check the command line and both config files for a User option.
None of the .service files contains a "User" option. (And systemd complains if you try to add one.)
You should not add a User option to the systemd service file.
Please post your configuration file /etc/tor/torrc (without sensitive content like password hashes)