I just set up a new BE85 system consisting of 2 Deco units and I keep getting an unstable Internet connection (across multiple devices and OS), this happens via cable or wireless, I also turned off the satellite Deco but it is not the cause of the problem.

I'm connecting the main Deco directly to a Huawei ONT, the Operation Mode is set to Wi-Fi Router, my ISP uses VLAN (VLAN ID: 10, Priority: 0) with Dynamic IP (IPV4), the router is able to acquire an Internet IP and even execute a speed test, however, it is very intermittent, it takes many retries to get a 2 GB file downloaded successfully and it never works in one go.

I was using an Orbi RBK50, with the same exact setup, (Orbi -> ONT using VLAN), and I never had any issues before.

Deco Log (around disconnect time):

Sun Dec  3 13:09:10 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:14 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:15 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:09:18 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:22 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:25 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:25 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:09:28 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:28 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:32 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:35 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:09:36 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:40 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:44 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:45 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:09:48 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:52 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:55 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:55 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:09:58 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:09:58 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:02 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:05 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:10:06 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:09 2023 daemon.notice nrd[24995]: ar_apinfo_collect[line 1392]: AP sync timer expires!
Sun Dec  3 13:10:10 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:14 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:16 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:10:18 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:22 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:25 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:26 2023 daemon.err standby: there are more than one device

Sun Dec  3 13:10:26 2023 user.err IMPROXY: ERROR[send_igmp_mld_query@307]: mld query: sendmsg failed: Invalid argument
Sun Dec  3 13:10:26 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:28 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:28 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:29 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:29 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.252 is Local Network Control Block
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.250 is Local Network Control Block
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.251 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:31 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.252 is Local Network Control Block
Sun Dec  3 13:10:32 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:32 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:32 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:32 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.249 is Local Network Control Block
Sun Dec  3 13:10:33 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:33 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:34 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:35 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@245]: Group address 224.0.0.251 is Local Network Control Block
Sun Dec  3 13:10:35 2023 user.notice IMPROXY: INFO[imp_verify_multicast_addr@258]: Group address 239.255.255.250 belongs to IPv4 Local Scope.
Sun Dec  3 13:10:36 2023 daemon.err miniupnpd[25320]: sendto(udp_notify=9, [::5291:e3ff:fe8c:6b72]): Network unreachable
Sun Dec  3 13:10:36 2023 daemon.err standby: there are more than one device

Wireshark screenshot before the disconnect: