You have to quit it and reopen it. Not sure why it bothers running in the background. Maybe it doesn’t like network shares, or it thinks it isn’t accessible because it opened before the network share was available. That is the last time I rebooted.
Be warned though, if you have Comcast and are only paying 50 bucks or less a month, your internet will barely work while backing up your photos. Unless you use a firewall and limit it to upload at only 50 kb/s.