Ubisoft says that, should the error keep occurring outside of an outage or maintenance, players should check their connectivity troubleshooter which, in our experience, doesn't often resolve the issue.
Rainbow Six Siege Error 3-0x0001000b is, according to the official pages, 'an error regarding the connection to the Ubisoft servers,' which means that if this thing keeps popping up, it's pretty likely that the problem is not on your end at all.
