I had typed everything below, then I saw your post about how you solved your problem. That's good. But, you might want to read what I wrote below, and even if you don't do the re-installation of Sierra, it is still good reference stuff, especially if you have issue again.
Also, a new version of Sierra, OS 10.12.3, came out last week. You can download the Combo Updater from here:
https://support.apple.com/kb/DL1905?locale=en_US
OK, thanks for that. However, not doing any disk cleanup on a daily basis, and periodically not doing any disk cleanup/maintenance/repairs is asking for trouble. At least, though, you are using Time Machine for backups. Is that to an external device?
Additionally, how
exactly did you upgrade to Sierra? Again, did you just let Sierra "overwrite" whatever prior OS you were using?
And one other thing, are you using any third party software? If you are, some of them might not be compatible with Sierra (assuming you were using such programs prior to upgrading), and thus would need to also be upgraded.
Now, from what I am seeing, it might be best if you do a clean installation of Sierra. The steps involved would be:
1. Go to the App store, and download the latest version of Sierra (V10.12.3 came out last week).
2. Make one more Time Machine backup, and also for the OS 10.12.3 file you download from the App store, "copy" it to another place on your external drive (this might require partitioning the drive, leaving the Time Machine backup as is, but on a new partition).
3. Boot your machine to the (hidden) Recovery HD partition. This link describes how to do that, and what is on that partition:
https://support.apple.com/en-us/HT201314
4. Note the 4th choice on that menu, Disk Utility. Select that, and have it Erase and Format your internal drive.
5. After that is done, select #2, "Reinstall the Mac OS". What I am not sure of is the actual process that entails. Ideally, it would find that V10.12.3 download you did previously. (I do this process entirely different, so that is why I am unsure). Hopefully, that will install the latest version of Sierra, OS 10.12.3.
6. When that completes, I believe you'll be offered the opportunity, via Migration Assistant, to "migrate"/copy needed "stuff" from your Time Machine backup (and thus you would not need to select the first choice on that screen. That choice of Migration Assistant is typically what comes up after an installation on the Mac OS (and that has been my experience, even with the other way I do this process).
7. After completion, restart your machine. You should be good to go.
Also, you really should start doing daily disk cleanup, and periodic disk cleanup/maintenance/repairs. While SSDs have less mechanical parts than a standard HDD, it's still both beneficial and necessary to do disk-related maintenance "stuff". There are both free and commercial products you can use to assist with those tasks. Myself, I use the excellent freeware program Onyx (been around a long, long time, is a solid performer, and has had numerous stellar reviews), and the commercial product TechTool Pro (another excellent mainstay in the Mac "world").
