Never seen that. My guess would be that it is some app that does it....
Say some app that fails to do whatever it tries to and is signalling for you to fix it. e.g. a mail app failing to communicate with the mail-server
When you say restart, is it just a Press power select Restart, or is it a hold power down for some 10 secs? The later does a deeper boot. (and is simple and non-destructive so try that first)
If that does not fix it I would try to stop apps (Settings, Apps, See all apps, find and click app, click Force Stop) on any newly installed or newly updated app, to see see if t