"Wrong social identity for user account" easy login with Facebook (iOS)

I started to get fault “Wrong social identity for user account” when trying to login with Facebook (via easyLoginWithFacebookFieldsMapping) several days ago, login fails each time. It worked before and I haven’t changed anything in the code.
What could possibly have caused this issue and what exactly does this fault mean?
Is it possible that this issue occurred because I had used the same Facebook app credentials (app ID, app secret) in different backendless apps (for testing purposes)? However, I have already changed the credentials to the default ones and the problem persists.

I have found the same topic http://support.backendless.com/t/wrong-social-identity-for-user-account-when-trying-to-login-with-facebook and close this one, as duplicate.