i get similar issue when setting static ip on my ax58u.
Dec 27 12:25:32 kernel: ^[[0;33;41m[ERROR mcast] bcm_mcast_netlink_process_snoop_cfg,926: interface 20 could not be found^[[0m
Dec 27 12:25:19 rc_service: httpds 1430:notify_rc restart_net_and_phy
Dec 27 12:25:21 iTunes: daemon is stoped
Dec 27 12:25:21 FTP Server: daemon is stoped
Dec 27 12:25:21 Samba Server: smb daemon is stoped
Dec 27 12:25:22 kernel: wl0: set timeout 5 secs to wait dev reg finish
Dec 27 12:25:24 kernel: wl0: set timeout 5 secs to wait dev reg finish
Dec 27 12:25:29 nat: apply nat rules (/tmp/nat_rules_eth4_eth4)
Dec 27 12:25:29 kernel: port_generic_stop 561 skip turnning off power on eth3 here
Dec 27 12:25:29 kernel: port_generic_stop 561 skip turnning off power on eth2 here
Dec 27 12:25:29 kernel: port_generic_stop 561 skip turnning off power on eth1 here
Dec 27 12:25:29 kernel: port_generic_stop 561 skip turnning off power on eth0 here
Dec 27 12:25:29 kernel: ubi2: attaching mtd10
Dec 27 12:25:29 kernel: ubi2: scanning is finished
Dec 27 12:25:29 kernel: ubi2: attached mtd10 (name "misc1", size 8 MiB)
Dec 27 12:25:29 kernel: ubi2: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
Dec 27 12:25:29 kernel: ubi2: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
Dec 27 12:25:29 kernel: ubi2: VID header offset: 2048 (aligned 2048), data offset: 4096
Dec 27 12:25:29 kernel: ubi2: good PEBs: 64, bad PEBs: 0, corrupted PEBs: 0
Dec 27 12:25:29 kernel: ubi2: user volume: 1, internal volumes: 1, max. volumes count: 128
Dec 27 12:25:29 kernel: ubi2: max/mean erase counter: 10/4, WL threshold: 4096, image sequence number: 1108767370
Dec 27 12:25:29 kernel: ubi2: available PEBs: 0, total reserved PEBs: 64, PEBs reserved for bad PEB handling: 4
Dec 27 12:25:29 kernel: ubi2: background thread "ubi_bgt2d" started, PID 24942
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): background thread "ubifs_bgt2_0" started, PID 24958
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): UBIFS: mounted UBI device 2, volume 0, name "nvram"
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): LEB size: 126976 bytes (124 KiB), min./max. I/O unit sizes: 2048 bytes/2048 bytes
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): FS size: 5840896 bytes (5 MiB, 46 LEBs), journal size 1396736 bytes (1 MiB, 11 LEBs)
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): reserved for root: 0 bytes (0 KiB)
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): media format: w4/r0 (latest is w4/r0), UUID AF9E64C7-2546-4160-94B7-C0D3AFA3E6D3, small LPT model
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): un-mount UBI device 2
Dec 27 12:25:30 kernel: UBIFS (ubi2:0): background thread "ubifs_bgt2_0" stops
Dec 27 12:25:30 kernel: ubi2: detaching mtd10
Dec 27 12:25:30 kernel: ubi2: mtd10 is detached
Dec 27 12:25:32 watchdog: restart httpd
Dec 27 12:25:32 rc_service: watchdog 1440:notify_rc stop_httpd
Dec 27 12:25:32 rc_service: waitting "restart_net_and_phy" via ...
Dec 27 12:25:32 kernel: Register interface [wl1.1] MAC: a8:5e:45:ed:de:7d
Dec 27 12:25:32 kernel: Register interface [wl1.2] MAC: a8:5e:45:ed:de:7e
Dec 27 12:25:32 kernel: IGMP Query send failed
Dec 27 12:25:32 kernel: IGMP Query send failed
Dec 27 12:25:32 kernel: CPU: 1 PID: 25029 Comm: networkmap Tainted: P O 4.1.52 #2
Dec 27 12:25:32 kernel: Hardware name: Generic DT based system
Dec 27 12:25:32 kernel: task: d5045000 ti: d366a000 task.ti: d366a000
Dec 27 12:25:32 kernel: PC is at 0x174c4
Dec 27 12:25:32 kernel: LR is at 0xb6d9dab0
Dec 27 12:25:32 kernel: pc : [<000174c4>] lr : [<b6d9dab0>] psr: 200b0010
Dec 27 12:25:32 kernel: sp : be90ea10 ip : 000001dc fp : 00000001
Dec 27 12:25:32 kernel: r10: 0002da64 r9 : 0002da20 r8 : 00000000
Dec 27 12:25:32 kernel: r7 : 0002da30 r6 : 0002da94 r5 : 0002c000 r4 : 00000000
Dec 27 12:25:32 kernel: r3 : 0000d22c r2 : 0002da84 r1 : 0000d32b r0 : 0000000a
Dec 27 12:25:32 kernel: Flags: nzCv IRQs on FIQs on Mode USER_32 ISA ARM Segment user
Dec 27 12:25:32 kernel: Control: 10c5387d Table: 1329004a DAC: 00000015
Dec 27 12:25:32 kernel: CPU: 1 PID: 25029 Comm: networkmap Tainted: P O 4.1.52 #2
Dec 27 12:25:32 kernel: Hardware name: Generic DT based system
Dec 27 12:25:32 kernel: [<c0026e60>] (unwind_backtrace) from [<c0022c38>] (show_stack+0x10/0x14)
Dec 27 12:25:32 kernel: [<c0022c38>] (show_stack) from [<c0445b3c>] (dump_stack+0x8c/0xa0)
Dec 27 12:25:32 kernel: [<c0445b3c>] (dump_stack) from [<c003aab0>] (get_signal+0x490/0x558)
Dec 27 12:25:32 kernel: [<c003aab0>] (get_signal) from [<c00221d0>] (do_signal+0xc8/0x3ac)
Dec 27 12:25:32 kernel: [<c00221d0>] (do_signal) from [<c0022658>] (do_work_pending+0x94/0xa4)
Dec 27 12:25:32 kernel: [<c0022658>] (do_work_pending) from [<c001f4cc>] (work_pending+0xc/0x20)
Dec 27 12:25:33 nat: apply redirect rules
Dec 27 12:25:34 avahi-daemon[25135]: WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Dec 27 12:25:35 avahi-daemon[25135]: Alias name "RT-AX58U" successfully established.
Dec 27 12:25:35 acsd: acsd_main_loop(1097): sync_id: 8095, status:1, misc.error/abort
Dec 27 12:25:35 acsd: eth5: selected channel spec: 0x1907 (9u)
Dec 27 12:25:35 acsd: eth5: Adjusted channel spec: 0x1907 (9u)
Dec 27 12:25:35 acsd: eth5: selected channel spec: 0x1907 (9u)
Dec 27 12:25:35 acsd: acs_set_chspec: 0x1907 (9u) for reason APCS_INIT
Dec 27 12:25:35 acsd: eth6: Selecting 5g band ACS policy
Dec 27 12:25:35 acsd: acsd_main_loop(1097): sync_id: 8095, status:1, misc.error/abort
Dec 27 12:25:35 nat: apply nat rules (/tmp/nat_rules_eth4_eth4)
Dec 27 12:25:35 acsd: acs_candidate_score_intf(992): eth6: intf check failed for chanspec: 0xe832
Dec 27 12:25:35 acsd: acs_candidate_score_bgnoise(1312): eth6: bgnoise check failed for chanspec: 0xe832
Dec 27 12:25:35 acsd: acs_candidate_score_txop(1563): eth6: txop check failed for chanspec: 0xe832
Dec 27 12:25:35 acsd: acs_candidate_score_intf(992): eth6: intf check failed for chanspec: 0xe932
Dec 27 12:25:35 acsd: acs_candidate_score_bgnoise(1312): eth6: bgnoise check failed for chanspec: 0xe932
Dec 27 12:25:35 acsd: acs_candidate_score_txop(1563): eth6: txop check failed for chanspec: 0xe932
Dec 27 12:25:35 acsd: acs_candidate_score_intf(992): eth6: intf check failed for chanspec: 0xea32
Dec 27 12:25:35 acsd: acs_candidate_score_bgnoise(1312): eth6: bgnoise check failed for chanspec: 0xea32
Dec 27 12:25:35 acsd: acs_candidate_score_txop(1563): eth6: txop check failed for chanspec: 0xea32
Dec 27 12:25:35 acsd: acs_candidate_score_intf(992): eth6: intf check failed for chanspec: 0xeb32
Dec 27 12:25:35 acsd: acs_candidate_score_bgnoise(1312): eth6: bgnoise check failed for chanspec: 0xeb32
Dec 27 12:25:35 acsd: acs_candidate_score_txop(1563): eth6: txop check failed for chanspec: 0xeb32
Dec 27 12:25:35 acsd: eth6: selected channel spec: 0xe832 (36/160)
Dec 27 12:25:35 acsd: eth6: Adjusted channel spec: 0xe832 (36/160)
Dec 27 12:25:35 acsd: eth6: selected channel spec: 0xe832 (36/160)
Dec 27 12:25:35 acsd: acs_set_chspec: 0xe832 (36/160) for reason APCS_INIT
Dec 27 12:25:36 wan: finish adding multi routes
Dec 27 12:25:38 RT-AX58U: start https:8443
Dec 27 12:25:38 RT-AX58U: start httpd:80
Dec 27 12:25:38 httpd: Succeed to init SSL certificate...8443
Dec 27 12:25:38 httpd: Succeed to init SSL certificate...80
Dec 27 12:25:40 wlceventd: wlceventd_proc_event(499): wl0.1: Auth 50
4:F7:AB:3F:5F, status: Successful (0)
Dec 27 12:25:40 wlceventd: wlceventd_proc_event(527): wl0.1: Assoc 50
4:F7:AB:3F:5F, status: Successful (0)
Dec 27 12:25:40 rc_service: watchdog 1440:notify_rc start_httpd
Dec 27 12:25:40 RT-AX58U: start https:8443
Dec 27 12:25:40 RT-AX58U: start httpd:80
Dec 27 12:25:40 kernel: The For ALL DEVICES flag of Prof 1 has been set to ENABLE
its possible its normal and the older routers don't log it? no idea. in my case the router doesn't reboot or lose wan.