Why do PlayerPrefs become empty when uploading a new WebGL game version to Facebook

PlayerPrefs works perfectly on a specific WebGL game version. Uploading a new game version to Facebook makes PlayerPrefs "forget" everything. If I got it right, WebGL PlayerPrefs is saved in indexdb under the Application.persistentDataPath but the Application.persistentDataPath is different between each game version on Facebook. Even when you upload the same game zip twice, each version have a different Application.persistentDataPath. Any idea how to upload a new game version to Facebook without clearing the whole users PlayerPrefs? Thanks!