Hey there! Let's break down why your PlayerPrefs aren't updating on mobile Unity builds—this is a super common gotcha, so don't worry, we'll get it sorted.

• You forgot to call PlayerPrefs.Save()
  This is by far the most frequent culprit! PlayerPrefs doesn’t write changes to disk automatically. You have to explicitly trigger the save after setting your values. For example:

  // Set your desired value
  PlayerPrefs.SetInt("HighScore", 250);
  // Critical line to persist changes to disk
  PlayerPrefs.Save();
  

  On mobile, if your app exits abruptly (like being force-closed by the system or user), unsaved changes will be lost entirely.

• Missing storage permissions (Android/iOS)
  Modern mobile OSes (Android 13+ and some iOS versions) require explicit storage permissions for apps to write persistent data. Even though PlayerPrefs is supposed to handle this under the hood, permission conflicts can block writes. Double-check your app's permission settings in the device settings menu, or verify that you’ve enabled the necessary permissions in Unity’s Player Settings (look under Player Settings > Android > Publishing Settings > Permissions for Android).

• Data type mismatch when accessing values
  If you set a value with one data type but try to retrieve it with another, you’ll get unexpected results that make it seem like the value never saved. For example:

  // Mistake: Setting a float but retrieving as an int
  PlayerPrefs.SetFloat("PlayerHealth", 75.5f);
  int health = PlayerPrefs.GetInt("PlayerHealth"); // Returns 0, not 75
  

  Always pair SetX() methods with the matching GetX() method for the same key.

• Case-sensitive or typo-ridden key names
  PlayerPrefs keys are case-sensitive! If you save a value with PlayerPrefs.SetString("PlayerName", "Bob") but try to fetch it with PlayerPrefs.GetString("playername"), you’ll only get the default value instead of your saved data. Double-check all key names for consistency.

• Mobile OS caching delays
  Some mobile platforms cache disk writes to boost performance, so the PlayerPrefs file might not update immediately after you call Save(). If you’re manually checking the file right after closing the app, wait a minute or two before verifying, or test by reloading the app and retrieving the value directly in code instead of checking the file.

• App data was cleared or reinstalled
  If you uninstalled and reinstalled the app, or cleared its data via device settings, all PlayerPrefs values will be wiped. Make sure you’re testing with a consistent app installation that hasn’t had its data reset.

内容的提问来源于stack exchange，提问作者Oliver Sinnassamy