I first experienced this a couple days ago, but assumed it was a fluke.
When I click the Log Out button, it does appear to log me out. However, if I then navigate back to the RB7 login URL, I am logged immediately into my account again. (I had been intending to log into a sub-account). Very odd. I am on a Mac using the latest version of Firefox (66.0.5 as of this writing)
Note that I have not yet attempted to close the browser to see if that has any effect, but the browser has been closed (and the computer shut down) many times since I first encountered this issue, so it clearly isn’t a permanent fix.