My direction from support was to:
1.) Go into home phrase director (if installed)
2.) Change all the selections to something different and save.
3.) Exit out of the Smartthings app
4.) I cleared Smartthings app cache (not sure if necessary)
5.) Open Smartthings app
6.) Go back into Home Phrase Director.
7.) Change all selections back to what makes sense (previous settings) and save.
This worked for me although I did have to do it twice.
EDIT: GREAT BIG FAIL. Right back to not working.
This morning at 10AM when I left home my mode was changed from Home Day to Away Night. I reset it manually and when I returned home mode changed from Away Day to Home Night. I repeat. That was this morning between 9-11AM
I was told the issue was the Nest device and needed to remove all references to this device in each of my phases. Problem is , none of my phases reference the NEST.
Anyhoo… glad to know I am not alone.
Does that make any sense in your configuration, or do you think Tech Support was just grasping for anything?
NO!!! Nest is just a “Thing” and not used anywhere in any phase, mode, app, etc… Not even sure why I bothered adding it to ST… 
Because I can?
This is a bad habit of Tech Support then, and affects us developers / power-users negatively…
ie, if our configuration includes any unsupported / unofficial Device Type Handlers, then we are often asked to remove them before they will make a serious attempt at problem resolution.
You can guess how quickly that gets out of hand!
Unfortunately, I think is the latter, because I’ve been dealing with the same issue and don’t have a Nest thermostat and NO other unsupported devices or apps AND yes, I did restart my hub several times!
I deleted home phrase director then reinstalled.
I’ll report back if this worked.
I’m having the same problem with other apps that rely on Sunrise / Sunset
Also I am having problems with apps using RunIn() commands firing early…
One that is set to run in 1200 seconds is running in 300
I hope this post doesnt jinx things but… 
I think things are running correctly again. Anyone else concur??
Similar problem here. I had my vacation house automatically switch to AWAY NIGHT mode at 9pm and then to AWAY mode at 4 am. Last week, it just quit working and and stayed in AWAY NIGHT mode. I have to manually switch it over. Could this be related or the same problem? Anyone find a reliable way to fix?
UPDATE: I used their chat service, they confirmed my mode change quit working as intended about 9 days ago (last day to work was 8-22-15- sounds like similar timing to OP failure). They told me to change the time to 1 minute later (4:01 am), save it, then set it back to original time (4:00 am)and save it. Apparently, it forces a re-scheduling. They confirmed it now was scheduled to change at 4:00am. I indicated this seems odd, the fix here is just a temporary workaround. They said they were “looking into” the problem. I do like the ready help, but the glitch seems pretty serious to me.