Are you talking about webfonts? If yes, then maybe your smartphone has no internet connection at that time.
Even if you download the font on your machine, you won't have the desired effect because not any device will have that stored, so it will revert back to default.
Phone is connected to data...that should be enough right? Yeah I just see a default font of some sort. I could've sworn at some point I had it right in a previous build because my screen shots I took from the phone awhile back have the font I want it to be....maybe something is odd on my device itself?