There are a couple of things that commonly cause this.
High seasonal use
There's an old value cached in your Nest thermostat
This issue has popped up for some Skylark users since Nest's recent update in November 2016 - fear not, though, here's an effective help article that addresses this issue (hint: have you tried turning your Nest off, then on again?) ;)
A Manual Schedule in your Nest is overriding your status
Since Nest's November update, Manual Schedules are frequently overriding whatever status your Nest is put into via Skylark. In cases like this, we recommend you clear all manual schedules off your Nest, since Skylark can now control this based on whether or not you're home. Here's a link from Nest's support forum on how to clear a Manual Schedule.
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