Textures suddenly failing to load on iOS during long session

I am experiencing an issue where textures will suddenly fail to load on iOS after a long playthrough session. The objects will appear with the correct shader, but without the textures.

The textures loaded perfectly for about an hour of playtime. Suddenly, a few objects appeared in the scene untextured. When the player loaded a different scene, more objects appeared untextured. However, the problem solved itself when the player loaded a third scene.

This seems to be some sort of memory issue, but I have no idea where to start investigating. This is the first time I have seen this in months of testing. Does this issue seem familiar to anyone? Thank you very much for any help or ideas.

Device: iPhone 5s running iOS 9.2.1; Unity version: 5.3.2f1 Personal;