Reproduction steps:
1. Open the attached project.
2. Make sure IL2CPP is selected and Strip engine code checkbox is selected in the Player Settings.
3. Build the project for iOS.
4. Select Product > Archive in the Xcode.
5. Export the archive when project builds through the pop-up window.
6. Open the package and extact the Unity-iPhone.ipa file.
7. Open the Payload folder.
8. Inspect the Resync file (RMB > Show Package Contents).
9. Open resynth file with a text editor.
10. Look for RakNet, Hashtable, UnityWebRequest, NetworkPlayer, Physics, Physics2D references.
- The game doesn't use these features.

Resolution:
Some items should be fixed in newer Unity versions, some will get better in the future, and some can't really be helped.