To reproduce:
1. Open attached repro.unitypackage. It's a project that has a few cubes in a scene. The cubes have different materials.
2. Build & run for WP8
3. Pause
4. Resume the app
5. Notice that this takes a lot more time on some devices (8.612 seconds instead of 2.616)

Reproduced with Lumia 630, 530
Cannot be reproduced when building for the WP8.1 platform