[Remote access IPsec] Can't establish a connection-IKE port not opened (3 IPsec tunnels already operative)

Hi everybody,

We're facing this weird issue on a Sophos XGS 3300 (SFOS 19.0.0 GA-Build317) when we try to connect from remote site via Sophos Connect, I tried to unlock by hand the ports, remake the policy but nothing happens, even called to the ISP and for what they said they didn't unlocked anything.

Anyway the issue is really weird because there are already 3 IPsec site to site tunnels fully operative from this firewall to the branch offices and they work pretty well.

FYI the WAN where the IPsec connection happens is a PPPoE but I don't think it matters.

Here's some logs from Sophos Connect client:

2022-07-15 05:36:29PM 14[CFG] vici initiate CHILD_SA 'RemotoAccessIpsec-tunnel-1'
2022-07-15 05:36:29PM 10[IKE] <RemotoAccessIpsec|31> initiating Main Mode IKE_SA RemotoAccessIpsec[31] to xxx.xxx.xxx.xxx
2022-07-15 05:36:29PM 10[ENC] <RemotoAccessIpsec|31> generating ID_PROT request 0 [ SA V V V V V ]
2022-07-15 05:36:29PM 10[NET] <RemotoAccessIpsec|31> sending packet: from 192.168.1.xxx[58898] to xxx.xxx.xxx.xxx[500] (180 bytes)
2022-07-15 05:36:32PM 13[IKE] <RemotoAccessIpsec|31> sending retransmit 1 of request message ID 0, seq 1
2022-07-15 05:36:32PM 13[NET] <RemotoAccessIpsec|31> sending packet: from 192.168.1.xxx[58898] to xxx.xxx.xxx.xxx[500] (180 bytes)
2022-07-15 05:36:38PM 10[IKE] <RemotoAccessIpsec|31> sending retransmit 2 of request message ID 0, seq 1
2022-07-15 05:36:38PM 10[NET] <RemotoAccessIpsec|31> sending packet: from 192.168.1.xxx[58898] to xxx.xxx.xxx.xxx[500] (180 bytes)
2022-07-15 05:36:50PM 13[IKE] <RemotoAccessIpsec|31> giving up after 2 retransmits
2022-07-15 05:36:50PM 13[IKE] <RemotoAccessIpsec|31> establishing IKE_SA failed, peer not responding
2022-07-15 05:36:50PM 15[CFG] vici terminate IKE_SA 'RemotoAccessIpsec'
2022-07-15 05:36:50PM 11[ESP] unsupported IP version
2022-07-15 05:36:50PM 20[KNL] interface 17 'Sophos TAP Adapter' changed state from Up to Down
2022-07-15 05:36:51PM 14[CFG] unloaded shared key with id 'RemotoAccessIpsec-psk-id'
2022-07-15 05:36:51PM 15[CFG] unloaded shared key with id 'RemotoAccessIpsec-user-id'

Any idea?

Thank you