Asus DSL-N17U looses Public IP, then NAT IP

[alxnt]

Hi, I'm new here.
I have an issue as title says.
What I will describe below happens both in bridge mode and with asus on its own on the line.
I have set an ISP's zte h288 bridged with the asus n17u through ethernet wan.
Everything works fine but around midnight devices suddenly loose internet connection and when I log in the interface the internet ip is 10.99.x.x.
If I reboot the device or terminate wan connection and then just reconnect it gets a normal ip.
What I have tried:

• in wan menu various values in echo interval and max failures fields such as 0, 4 or 6, 10
• in extra pppd options, the above settings, as a command ( lcp-echo-interval 0 lcp-echo-failure 4)
• completely disable "internet detection" setting as I had seen many PAD0 errors
• various dns for wan(cloudflare, google etc)
• username.ath.forthnet.gr and username.ath.forthnet.gr@forthnet.gr in pppoe username
• ipv4/ipv6 mode with hope that ipv6 could be useful as failover

Also DSLAM is broadcom and asus is mediatek.
Is there anything else I can try to fix this?

 

[degrub]

Have you talked to your ISP about what there network is doing around midnight ?

You may be able to use double NATing to avoid the issue.

 

[alxnt]

Have you talked to your ISP about what there network is doing around midnight ?

You may be able to use double NATing to avoid the issue.

Yes they said that they don't see any problem. Can you tell me how to do this?

 

[degrub]

change the ISP device back to router.
set up your router to get its IP address from the ISP device.

 

[alxnt]

I changed on asus the custom dns(cloudflare or google) to auto(isp) and connection is rock solid stable more than a week. How dns can affect affect it?