Sorry not am expert but...... I suffered with TM being interrupted by what I thought was the Mac going to sleep. I set the energy saver to "Never got to sleep" but would come back to the Mac and it was back to "log in" and the TM action had been stopped. Eventually I realised in the Security settings that the box "Log Out (after so many minutes) was ticked. It happened to be set to 32 minutes Tony

I suffered with Time Machine being interrupted by what I thought was the Mac going to sleep. I set the energy saver to "Never got to sleep" but would come back to the Mac and it was back to "log in" and the Time Machine action had been stopped. Eventually I realized in the Security settings that "Log Out (after so many minutes) was checked. After unchecking this option I was able to stay logged in.