Mobile data not being saved on all devices

I made a game for android (Blinkies, shameless plug) and I save game data as described in the Unity "Persistence" Tutorial. For some phones, I believe an HTC was one of them, the data is not saved or it is being deleted. The file exists but the data is empty. I know this because the file saves the index of the color for the various parts of the character. The first color, index 0, is red. When the people with the problem launch the game (any launch after the initial launch) their character is all red; meaning the save file is being read and the data is used to set the color of the character. Otherwise, if no file existed, the character would be default grey. So I am thinking the data is holding null values and gets read as 0. I should note, the file does not get created until the player changes their character's color.

For most phones I am not having any problems. But a small few is still too many. Can anyone shed some light on a cause and/or solution to this problem?

I am currently trying to get the OS for these varying devices with the problems, but one person told me it was a "new" phone (I know that doesn't help, sorry)

Thanks for any input you may have or any related experiences.