I’m assuming your description of your setup from your previous post remains accurate? ARC Movistar Router configuration (ESP) - #25 by francisco_gaston
To clarify, your ISP has provided a dedicated external IP address. After disabling the VPN on both your Core and iPhone and setting a manual port forwarding rule in your Movistar router, ARC was functioning outside the home via cellular data.
However, if you close ARC outside the home, it will fail to connect to your Core unless you reinstall? Does ARC freeze or hang, or do you receive any warnings before having to reinstall? A precise description of the symptoms will help us pinpoint the issue in logging.
Recent diagnostics confirm that ARC is losing connection to your Core when connected via cellular data and timing out when attempting to log back in. Are there any diagnostics displayed in Roon → Settings → Roon ARC? If port forwarding is still configured correctly, then the remaining possibilities are memory pressure on the phone (there’s evidence of this in logging) or the VPN continuing to interfere with ARC.