We test each SpiderOak ONE release on the current stable version of macOS and the most recent previous one. As of July 2017, that means 10.12 Sierra and 10.11 El Capitan. These are the versions for which we provide official support.
We regularly receive reports of ONE running fine on macOS 10.8 Mountain Lion, 10.9 Mavericks, and 10.10 Yosemite. We no longer test on them however and so cannot offer advanced troubleshooting for them.
SpiderOak ONE is not yet compatible with macOS 10.13 High Sierra beta. We expect to have it working on or before 10.13's non-beta release in fall 2017. This is a common problem on beta releases of operating systems, as they are constantly changing and thus present an ever-moving target. For that reason we do not officially support beta versions of Mac or any operating system.