I just bumped into the same issue with a fresh install of redis 5.0.3 from debian 10.1 packages repository.
For me the solution was to give access to the config file (read) and the log file (read-write) to user redis.
chown -R redis:redis /var/log/redis
chmod -R u+rwX,g+rwX,u+rx /var/log/redis
chmod +r /etc/redis/redis.conf