from the logread, seems there is crash:
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.973719] WARNING: CPU: 0 PID: 996 at /usr/src/kernel/net/netfilter/nf_nat_core.c:393 nf_nat_setup_info+0x88/0x7c4()
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.973734] Modules linked in: cfg80211
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.973772] CPU: 0 PID: 996 Comm: kworker/u2:6 Not tainted 3.18.131 #1
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.973804] Workqueue: uether process_rx_w
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.973825] ------------[ cut here ]------------
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.977424] WARNING: CPU: 0 PID: 996 at /usr/src/kernel/kernel/locking/mutex.c:870 mutex_trylock+0x78/0x174()
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.987426] DEBUG_LOCKS_WARN_ON(in_interrupt())
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.991693] Modules linked in: cfg80211
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 40.995647] CPU: 0 PID: 996 Comm: kworker/u2:6 Not tainted 3.18.131 #1
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.002224] Workqueue: uether process_rx_w
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.006269] [<c0014428>] (unwind_backtrace) from [<c00122ac>] (show_stack+0x10/0x14)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.014019] [<c00122ac>] (show_stack) from [<c001f490>] (warn_slowpath_common+0x60/0x80)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.022110] [<c001f490>] (warn_slowpath_common) from [<c001f4dc>] (warn_slowpath_fmt+0x2c/0x3c)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.030769] [<c001f4dc>] (warn_slowpath_fmt) from [<c0790450>] (mutex_trylock+0x78/0x174)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.038890] [<c0790450>] (mutex_trylock) from [<c001acbc>] (sierra_smem_errdump_save_frame+0x20/0x124)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.048218] [<c001acbc>] (sierra_smem_errdump_save_frame) from [<c00144c0>] (unwind_backtrace+0x98/0x128)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.057766] [<c00144c0>] (unwind_backtrace) from [<c00122ac>] (show_stack+0x10/0x14)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.065490] [<c00122ac>] (show_stack) from [<c001f490>] (warn_slowpath_common+0x60/0x80)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.073559] [<c001f490>] (warn_slowpath_common) from [<c001f540>] (warn_slowpath_null+0x18/0x20)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.082334] [<c001f540>] (warn_slowpath_null) from [<c068201c>] (nf_nat_setup_info+0x88/0x7c4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.090930] [<c068201c>] (nf_nat_setup_info) from [<c06e097c>] (nf_nat_masquerade_ipv4+0x13c/0x158)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.099913] [<c06e097c>] (nf_nat_masquerade_ipv4) from [<c06e3304>] (masquerade_tg+0x40/0x60)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.108475] [<c06e3304>] (masquerade_tg) from [<c06e14b4>] (ipt_do_table+0x694/0x790)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.116271] [<c06e14b4>] (ipt_do_table) from [<c06dd4b4>] (nf_nat_ipv4_fn+0x118/0x210)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.124171] [<c06dd4b4>] (nf_nat_ipv4_fn) from [<c06dd660>] (nf_nat_ipv4_out+0x3c/0xec)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.132152] [<c06dd660>] (nf_nat_ipv4_out) from [<c06640f4>] (nf_iterate+0x68/0xb4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.139795] [<c06640f4>] (nf_iterate) from [<c066419c>] (nf_hook_slow+0x5c/0x110)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.147265] [<c066419c>] (nf_hook_slow) from [<c0698700>] (ip_output+0xb8/0xd4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.154561] [<c0698700>] (ip_output) from [<c063e080>] (__netif_receive_skb_core+0x400/0x50c)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.163066] [<c063e080>] (__netif_receive_skb_core) from [<c0640118>] (process_backlog+0x70/0x110)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.172003] [<c0640118>] (process_backlog) from [<c063fa60>] (net_rx_action+0x80/0x158)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.179946] [<c063fa60>] (net_rx_action) from [<c0021f20>] (__do_softirq+0x180/0x1e8)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.187797] [<c0021f20>] (__do_softirq) from [<c002205c>] (do_softirq+0x44/0x54)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.195173] [<c002205c>] (do_softirq) from [<c0640658>] (netif_rx_ni+0x34/0x70)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.202471] [<c0640658>] (netif_rx_ni) from [<c04372cc>] (process_rx_w+0x170/0x1d4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.210109] [<c04372cc>] (process_rx_w) from [<c0031014>] (process_one_work+0x1bc/0x2e0)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.218138] [<c0031014>] (process_one_work) from [<c0031dd0>] (worker_thread+0x2dc/0x3b8)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.226337] [<c0031dd0>] (worker_thread) from [<c003567c>] (kthread+0xc8/0xd4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.233578] [<c003567c>] (kthread) from [<c000e798>] (ret_from_fork+0x14/0x3c)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.240741] ---[ end trace 9aeba0951e9fb07b ]---
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.245313] [<c0014428>] (unwind_backtrace) from [<c00122ac>] (show_stack+0x10/0x14)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.253077] [<c00122ac>] (show_stack) from [<c001f490>] (warn_slowpath_common+0x60/0x80)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.261155] [<c001f490>] (warn_slowpath_common) from [<c001f540>] (warn_slowpath_null+0x18/0x20)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.269873] [<c001f540>] (warn_slowpath_null) from [<c068201c>] (nf_nat_setup_info+0x88/0x7c4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.278512] [<c068201c>] (nf_nat_setup_info) from [<c06e097c>] (nf_nat_masquerade_ipv4+0x13c/0x158)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.287554] [<c06e097c>] (nf_nat_masquerade_ipv4) from [<c06e3304>] (masquerade_tg+0x40/0x60)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.296045] [<c06e3304>] (masquerade_tg) from [<c06e14b4>] (ipt_do_table+0x694/0x790)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.303856] [<c06e14b4>] (ipt_do_table) from [<c06dd4b4>] (nf_nat_ipv4_fn+0x118/0x210)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.311755] [<c06dd4b4>] (nf_nat_ipv4_fn) from [<c06dd660>] (nf_nat_ipv4_out+0x3c/0xec)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.319697] [<c06dd660>] (nf_nat_ipv4_out) from [<c06640f4>] (nf_iterate+0x68/0xb4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.327382] [<c06640f4>] (nf_iterate) from [<c066419c>] (nf_hook_slow+0x5c/0x110)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.334845] [<c066419c>] (nf_hook_slow) from [<c0698700>] (ip_output+0xb8/0xd4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.342142] [<c0698700>] (ip_output) from [<c063e080>] (__netif_receive_skb_core+0x400/0x50c)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.350650] [<c063e080>] (__netif_receive_skb_core) from [<c0640118>] (process_backlog+0x70/0x110)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.359544] [<c0640118>] (process_backlog) from [<c063fa60>] (net_rx_action+0x80/0x158)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.367576] [<c063fa60>] (net_rx_action) from [<c0021f20>] (__do_softirq+0x180/0x1e8)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.375383] [<c0021f20>] (__do_softirq) from [<c002205c>] (do_softirq+0x44/0x54)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.382759] [<c002205c>] (do_softirq) from [<c0640658>] (netif_rx_ni+0x34/0x70)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.390015] [<c0640658>] (netif_rx_ni) from [<c04372cc>] (process_rx_w+0x170/0x1d4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.397689] [<c04372cc>] (process_rx_w) from [<c0031014>] (process_one_work+0x1bc/0x2e0)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.405768] [<c0031014>] (process_one_work) from [<c0031dd0>] (worker_thread+0x2dc/0x3b8)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.413935] [<c0031dd0>] (worker_thread) from [<c003567c>] (kthread+0xc8/0xd4)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.421126] [<c003567c>] (kthread) from [<c000e798>] (ret_from_fork+0x14/0x3c)
Jan 21 12:40:07 swi-mdm9x28-wp user.warn kernel: [ 41.428282] ---[ end trace 9aeba0951e9fb07c ]---
Jan 21 12:40:46 swi-mdm9x28-wp user.info Legato: INFO | supervisor[835]/supervisor T=main | supervisor.c HandleRebootExpiry() 534 | Expired reboot timer
Jan 21 12:41:27 swi-mdm9x28-wp user.info kernel: [ 121.441244] sierra_startup_monitor
Jan 21 12:43:34 swi-mdm9x28-wp authpriv.info dropbear[2046]: Child connection from 192.168.2.3:53234
Jan 21 12:43:35 swi-mdm9x28-wp authpriv.notice dropbear[2046]: Auth succeeded with blank password for 'root' from 192.168.2.3:53234
Jan 21 12:43:35 swi-mdm9x28-wp authpriv.warn dropbear[2047]: lastlog_perform_login: Couldn't stat /var/log/lastlog: No such file or directory
Jan 21 12:43:35 swi-mdm9x28-wp authpriv.warn dropbear[2047]: lastlog_openseek: /var/log/lastlog is not a file or directory!
BTW, have you marked the system to be good by “update -g” after installing the modemdemo application?
Lastly, you can see here to modify wifi.sdef in order to embed your application in the legato image: