Only 1 camera works outside local network

[user_770699490549922_770699490549922]

I have 4 E1 Pro wifi enabled cameras and I'm using a VPN to access my cameras outside my local network (routing to local network with ZeroTier). I have activated rtsp and when I'm using my phone on 5G and using VLC, I can see the stream of all my 4 cameras. However, when I use the (iOS) reolink app, I can only see the stream of 1 of the 4 cameras. The other 3, I cannot connect to.

Of course, all 4 cameras have (to my knowledge) the exact same configuration (disabled UID, DHCP connexion with static IP for all 4 cameras...).

Any ideas why this behavior and how I can make all 4 cameras display on the reolink app ?