The servers at Apple are totally maxed out right now, so things that use those servers are sometimes taking an inordinate amount of time to get done. For example, I had to restore my iPhone 5 from a backup yesterday (not because of iOS 9 - a separate issue). I started the restore yesterday afternoon, and it finished around 4:00 pm today. When I originally set up this phone from a backup it took an hour.
I also can report that the download of the backup sped up as the day progressed.
So, the reason your device may not have backed up overnight like it usually does might be because it was in the queue, and simply did not get to the front of the line before you disconnected it from power this morning to use it. Had it been plugged in all night and all day today, there is a good chance it would have backed up.
Your Last Backup and Last Backup size under iOS 9 is 0 Bytes - but if you look at your Next Backup, it should be reflecting the total amount of storage that the items you have checked below add up to.
If you want to manually initiate a backup, then try again later tonight or over the weekend. If you leave your phone connected to power with Wifi and the Lock Screen on tonight, there is a good chance that tomorrow morning you will have seen that it has backed up.
Best of luck,
GB