Friend no longer appearing online after a change between two regions

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Currently, we have implemented an invite systems but since our players can play in different regions we added a check to make sure the inviting player's friend is in the same region.

If two players who are friends log-in, they will see each other online in their respective friend's list and can invite one another if they are both on the same region. However, if one friend changes to another region then change back to the original region they cannot invite any friends even if both are connected to the same region. The IsOnline boolean in their friends FriendInfo returns false.

I want to state that a players friends list is updated at regular intervals (every 3 seconds whilst the player is in PhotonNetwork.Lobbby). I also want to add that all players are connected to the same region for Photon Chat. This is because we want players to be able to see friends who are online even if they are not connected to the same region. For PUN players are able to choose which region they want to connect to (the best region is chosen as default).

My question is to know why this is occurring and how we could find a solution to this problem