I know the off-by-one date problem has been discussed before, but I have discovered, for my self anyway, why it sometimes appears hit-and-miss.
If I open Logos when the devotion was the last thing I was reading, all is OK. That is, reading a devotional, exiting Logos, and killing it from the taskbar. If I then open Logos, it opens to the devotional to the correct date. If I then go to the home page, the devotional date has changed to yesterday, even though I was just reading the devotional for today.
It appears that on freshly opening a devotional, Logos correctly determines the date, but going to the Home page has a different date determination method that is wrong.
It seems like they have the correct date calculation method, they just need to put it in the correct place(s).