Reproduction steps:
1. Open the attached project with 5.3 Unity version.
2. Navigate to Assets > Plugins > iOS > Flurry > iOS folder in the Project view.
3. Select every file one by one.
- Platform is set to iOS on every file.
4. Open the same project with 5.6 Unity version.
5. Repeat steps 2 and 3.
- Platform is set to Any Platform on some of the files.

Reproduced on:
5.6.2p4, 2017.3.0a1

Meta files break when using Editor versions in this order:
5.3 > 5.6
5.3 > 2017.3

Meta files don't break when using Editor versions in this order:
5.3 > 5.4 > 5.5 > 5.6
5.3 > 5.4 > 5.6
5.3 > 5.5 > 5.6