Why does the L2TP connection disappear on the TP-link TLWR-842ND(Openwrt) router?

Question

linux

Recently, the connection via the L2TP protocol (Beeline operator) began to disappear.
I am posting the latest logs, but I don’t know what else I need to post here, write what you need.
Please do not pay attention to the date, flew off, today's logs.

Sep 30 22:39:12 router daemon.notice netifd: Interface 'lan' is now up
Sep 30 22:39:12 router daemon.notice netifd: Interface 'loopback' is now up
Sep 30 22:39:13 router daemon.notice netifd: bee (971): Could not resolve server address
Sep 30 22:39:13 router daemon.notice netifd: wan (1011): udhcpc (v1.19.4) started
Sep 30 22:39:13 router daemon.notice netifd: wan (1011): Sending discover...
Sep 30 22:39:14 router user.notice ifup: Enabling Router Solicitations on lan (br-lan)
Sep 30 22:39:16 router daemon.notice netifd: wan (1011): Sending discover...
Sep 30 22:39:16 router daemon.notice netifd: wan (1011): Sending select for 10.108.42.81...
Sep 30 22:39:16 router daemon.notice netifd: wan (1011): Lease of 10.108.42.81 obtained, lease time 1019618
Sep 30 22:39:17 router daemon.notice netifd: Interface 'wan' is now up
Sep 30 22:39:18 router daemon.notice netifd: Interface 'bee' is now down
Sep 30 22:39:19 router daemon.crit xl2tpd[1371]: setsockopt recvref[30]: Protocol not available
Sep 30 22:39:19 router daemon.notice xl2tpd[1389]: Connecting to host tp.internet.beeline.ru, port 1701
Sep 30 22:39:19 router daemon.notice xl2tpd[1389]: Connection established to 10.255.255.244, 1701.  Local: 3516, Remote: 58094 (ref=0/0).
Sep 30 22:39:19 router daemon.notice xl2tpd[1389]: Calling on tunnel 3516
Sep 30 22:39:19 router daemon.notice xl2tpd[1389]: Call established with 10.255.255.244, Local: 64767, Remote: 27011, Serial: 1 (ref=0/0)
Sep 30 22:39:19 router daemon.notice pppd[1404]: pppd 2.4.5 started by root, uid 0
Sep 30 22:39:19 router daemon.notice pppd[1404]: Connect: l2tp-bee <--> 
Sep 30 22:39:19 router user.notice ifup: Enabling Router Solicitations on loopback (lo)
Sep 30 22:39:19 router daemon.notice pppd[1404]: PAP authentication succeeded
Sep 30 22:39:19 router daemon.notice pppd[1404]: local  IP address 128.71.79.82
Sep 30 22:39:19 router daemon.notice pppd[1404]: remote IP address 194.186.120.130
Sep 30 22:39:19 router daemon.notice pppd[1404]: primary   DNS address 195.239.238.211
Sep 30 22:39:19 router daemon.notice pppd[1404]: secondary DNS address 195.239.238.212
Sep 30 22:39:20 router daemon.notice netifd: Interface 'bee' is now up
Sep 30 22:39:22 router user.notice ifup: Allowing Router Advertisements on wan (br-wan)
Sep 30 22:39:26 router user.notice ifup: Enabling Router Solicitations on bee (l2tp-bee)
Oct  1 01:44:06 router daemon.notice pppd[1404]: Serial link appears to be disconnected.
Oct  1 01:44:06 router daemon.notice pppd[1404]: Connection terminated.
Oct  1 01:44:06 router daemon.notice pppd[1404]: Modem hangup
Oct  1 01:44:06 router daemon.notice netifd: Interface 'bee' has lost the connection
Oct  1 01:44:24 router daemon.notice xl2tpd[1389]: Maximum retries exceeded for tunnel 3516.  Closing.
Oct  1 01:44:44 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:45:04 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:45:24 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:45:44 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:46:04 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:46:24 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.
Oct  1 01:46:44 router daemon.warn xl2tpd[1389]: Host name lookup failed for tp.internet.beeline.ru.

Answer 1

Most often, problems do not arise due to the router. The reason is the fall of some beeline services. Output correct settings for fast reconnection. In particular

option metric '50' 
option reqopts 'routes msstaticroutes'

Sometimes the router does not fall off for months, sometimes dozens of times per evening.

Answer 2

Have you flashed Openwrt for a long time? He used to work fine, didn't he? I have the same router with Beeline L2TP stably started working only on beta firmware from TP-Link 3.12.23 Build 121206 Rel.58737n (Beta), which I had to roll back from WRT with a change of provider.
And, you have the second revision, as I understand it. I had a problem with the first one.