We have a 3910 vigor with two wan. One for pppoe and one for dhcp. The wan that is on dhcp restarts approximately every 10 minutes. The log shows some information but I have searched the internet without success. I have tried all the wan detection options with no success. Attached detailed log in case someone else has happened and has solved it.



<166>1 2021-06-24T02:56:45-04:00 172.16.2.1 DrayTek - - - DrayTek: Delete exist flowstate of BBG_Down ifno: 8 ...
<166>1 2021-06-24T02:56:45-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN 6 is down.
<150>1 2021-06-24T02:56:45-04:00 172.16.2.1 DrayTek - - - DrayTek: [WEB]Dynamic DNS Setup> Force Update
<141>1 2021-06-24T02:56:45-04:00 172.16.2.1 DrayTek - - - DrayTek: Delete exist flowstate of VPN ifno: 8 ....
<166>1 2021-06-24T02:56:46-04:00 172.16.2.1 DrayTek - - - DrayTek: ddns_SendHttpRequest(): Send Http Request to a258af0c#015
<166>1 2021-06-24T02:56:46-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN6 DHCP ==>XID = 0xfdaa7d07, Client IP = 0.0.0.0, Your IP = 0.0.0.0, Next server IP = 0.0.0.0, Relay agent IP = 0.0.0.0, Option:
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN6 DHCP <==XID = 0xfdaa7d07, Client IP = 0.0.0.0, Your IP = 89.35.62.154, Next server IP = 0.0.0.0, Relay agent IP = 0.0.0.0, Option:
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN6 DHCP ==>XID = 0xfdaa7d07, Client IP = 0.0.0.0, Your IP = 0.0.0.0, Next server IP = 0.0.0.0, Relay agent IP = 0.0.0.0, Option:
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: ddns_SendHttpRequest(): Send Http Request to a258af0c#015
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN6 DHCP <==XID = 0xfdaa7d07, Client IP = 0.0.0.0, Your IP = 89.35.62.154, Next server IP = 0.0.0.0, Relay agent IP = 0.0.0.0, Option:
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: Delete exist flowstate of BBG_UP ifno: 8 ...
<166>1 2021-06-24T02:56:47-04:00 172.16.2.1 DrayTek - - - DrayTek: WAN 6 is up.

Sounds like your connection is possibly physically dropping.
What settings are you using too see whether it's up or not.

We currently have a Unifiber ONT connected to the WAN and with a DHCP configuration and Vlan Tag 20. To rule out that it was the ONT's issue since it is our own. We switched to the operator's router which we put behind the WAN configuring the force in both DHCP and Static ip with the same result.