Remove and then reinsert the USB device. Now look in the router's System Log - General Log. The error messages might provide a clue to the problem.
Thanks, results follow, no change--still no device displayed in Network Map. Troubleshooting follows, flash drives are Lexar (2.0) and Sandisk (3.0). Log entries are above my level of comprehension.
Aug 18 06:38:13 WAN Connection: ISP's DHCP did not function properly.
Aug 18 06:38:14 nat: apply redirect rules
Aug 18 06:38:18 WAN Connection: Ethernet link up.
Aug 18 06:38:18 rc_service: wanduck 203:notify_rc restart_wan_if 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 9 for vlan2 mvlan_en 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 2 for vlan2 mvlan_en 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 13 for vlan2 mvlan_en 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 1 for vlan2 mvlan_en 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 4 for vlan2 mvlan_en 0
Aug 18 06:38:19 kernel: et0: et_mvlan_netdev_event: event 4 for vlan2 mvlan_en 0
Aug 18 06:38:22 rc_service: udhcpc 27890:notify_rc start_firewall
Aug 18 06:38:23 wan: finish adding multi routes
Aug 18 06:38:23 rc_service: udhcpc 27890:notify_rc stop_upnp
Aug 18 06:38:23 rc_service: waitting "start_firewall" via udhcpc ...
Aug 18 06:38:23 miniupnpd[13165]: shutting down MiniUPnPd
Aug 18 06:38:24 nat: apply nat rules (/tmp/nat_rules_vlan2_vlan2)
Aug 18 06:38:24 miniupnpd[27935]: version 1.9 started
Aug 18 06:38:24 miniupnpd[27935]: HTTP listening on port 59887
Aug 18 06:38:24 miniupnpd[27935]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 06:38:24 rc_service: udhcpc 27890:notify_rc start_upnp
Aug 18 06:38:24 rc_service: waitting "stop_upnp" via udhcpc ...
Aug 18 06:38:24 miniupnpd[27935]: shutting down MiniUPnPd
Aug 18 06:38:26 miniupnpd[27939]: version 1.9 started
Aug 18 06:38:26 miniupnpd[27939]: HTTP listening on port 36035
Aug 18 06:38:26 miniupnpd[27939]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 06:38:26 dhcp client: bound 71.11.37.188 via 71.11.32.1 during 3600 seconds.
Aug 18 06:38:27 WAN Connection: WAN was restored.
So now I have unplugged BOTH flash drives and installed the 3.0 drive in the 2.0 port. Now BOTH flash drives display in Network Map. Log follows:
Aug 18 09:30:43 rc_service: hotplug 31601:notify_rc restart_nasapps
Aug 18 09:30:43 hotplug[31600]: USB partition unmounted from /tmp/mnt/Lexar fail. (return -1, Bad file descriptor)
Aug 18 09:30:44 iTunes: daemon is stoped
Aug 18 09:30:44 FTP Server: daemon is stoped
Aug 18 09:30:44 Samba Server: smb daemon is stoped
Aug 18 09:30:44 kernel: gro disabled
Aug 18 09:30:44 Timemachine: daemon is stoped
Aug 18 09:30:44 rc_service: hotplug 31600:notify_rc stop_nasapps
Aug 18 09:30:44 rc_service: waitting "restart_nasapps" via ...
Aug 18 09:30:44 miniupnpd[27939]: shutting down MiniUPnPd
Aug 18 09:30:44 avahi-daemon[31612]: WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Aug 18 09:30:45 avahi-daemon[31612]: Alias name "RT-AC68P" successfully established.
Aug 18 09:30:56 kernel: scsi 5:0:0:0: Direct-Access SanDisk Ultra 1.00 PQ: 0 ANSI: 6
Aug 18 09:30:56 kernel: sd 5:0:0:0: Attached scsi generic sg0 type 0
Aug 18 09:30:56 kernel: sd 5:0:0:0: [sdb] 489160704 512-byte logical blocks: (250 GB/233 GiB)
Aug 18 09:30:57 kernel: sd 5:0:0:0: [sdb] Write Protect is off
Aug 18 09:30:57 kernel: sd 5:0:0:0: [sdb] Assuming drive cache: write through
Aug 18 09:30:57 kernel: sd 5:0:0:0: [sdb] Assuming drive cache: write through
Aug 18 09:30:57 kernel: sd 5:0:0:0: [sdb] Assuming drive cache: write through
Aug 18 09:30:57 kernel: sd 5:0:0:0: [sdb] Attached SCSI removable disk
Aug 18 09:31:11 kernel: scsi 6:0:0:0: Direct-Access Lexar USB Flash Drive 8.07 PQ: 0 ANSI: 4
Aug 18 09:31:11 kernel: sd 6:0:0:0: Attached scsi generic sg1 type 0
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] 31285248 512-byte logical blocks: (16.0 GB/14.9 GiB)
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] Write Protect is off
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] Assuming drive cache: write through
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] Assuming drive cache: write through
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] Assuming drive cache: write through
Aug 18 09:31:11 kernel: sd 6:0:0:0: [sdc] Attached SCSI removable disk
Aug 18 09:31:14 rc_service: skip the event: stop_nasapps.
Aug 18 09:31:14 kernel: gro enabled with interval 2
Aug 18 09:31:15 Samba Server: daemon is started
Aug 18 09:31:15 miniupnpd[31695]: version 1.9 started
Aug 18 09:31:15 miniupnpd[31695]: HTTP listening on port 41927
Aug 18 09:31:15 miniupnpd[31695]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 09:31:16 syslog: USB partition unmounted from /tmp/mnt/Lexar
Aug 18 09:31:16 rc_service: hotplug 31600:notify_rc restart_nasapps
Aug 18 09:31:16 iTunes: daemon is stoped
Aug 18 09:31:16 FTP Server: daemon is stoped
Aug 18 09:31:17 kernel: tfat warning (device sdc1, pid 31703): fat_fill_super(): FAT volume Lexar is dirty. You should unmount and repair it.
Aug 18 09:31:17 usb: USB vfat fs at /dev/sdc1 mounted on /tmp/mnt/Lexar.
Aug 18 09:31:17 Samba Server: smb daemon is stoped
Aug 18 09:31:17 kernel: gro disabled
Aug 18 09:31:17 Timemachine: daemon is stoped
Aug 18 09:31:17 miniupnpd[31695]: shutting down MiniUPnPd
Aug 18 09:31:17 kernel: gro enabled with interval 2
Aug 18 09:31:17 rc_service: hotplug 31673:notify_rc restart_nasapps
Aug 18 09:31:17 rc_service: waitting "restart_nasapps" via ...
Aug 18 09:31:17 avahi-daemon[31734]: WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Aug 18 09:31:17 Samba Server: daemon is started
Aug 18 09:31:18 miniupnpd[31743]: version 1.9 started
Aug 18 09:31:18 miniupnpd[31743]: HTTP listening on port 49584
Aug 18 09:31:18 miniupnpd[31743]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 09:31:18 avahi-daemon[31734]: Alias name "RT-AC68P" successfully established.
Aug 18 09:31:18 iTunes: daemon is stoped
Aug 18 09:31:18 FTP Server: daemon is stoped
Aug 18 09:31:19 Samba Server: smb daemon is stoped
Aug 18 09:31:19 kernel: gro disabled
Aug 18 09:31:20 Timemachine: daemon is stoped
Aug 18 09:31:20 miniupnpd[31743]: shutting down MiniUPnPd
Aug 18 09:31:20 kernel: gro enabled with interval 2
Aug 18 09:31:20 avahi-daemon[31761]: WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Aug 18 09:31:20 Samba Server: daemon is started
Aug 18 09:31:20 miniupnpd[31773]: version 1.9 started
Aug 18 09:31:20 miniupnpd[31773]: HTTP listening on port 46677
Aug 18 09:31:20 miniupnpd[31773]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 09:31:21 avahi-daemon[31761]: Alias name "RT-AC68P" successfully established.
Aug 18 09:31:23 kernel: tfat warning (device sdb1, pid 31780): fat_fill_super(): FAT volume is dirty. You should unmount and repair it.
Aug 18 09:31:23 usb: USB vfat fs at /dev/sdb1 mounted on /tmp/mnt/sdb1.
Aug 18 09:31:25 rc_service: hotplug 31640:notify_rc restart_nasapps
Aug 18 09:31:26 iTunes: daemon is stoped
Aug 18 09:31:26 FTP Server: daemon is stoped
Aug 18 09:31:27 Samba Server: smb daemon is stoped
Aug 18 09:31:27 kernel: gro disabled
Aug 18 09:31:27 Timemachine: daemon is stoped
Aug 18 09:31:27 miniupnpd[31773]: shutting down MiniUPnPd
Aug 18 09:31:27 kernel: gro enabled with interval 2
Aug 18 09:31:27 avahi-daemon[31812]: WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
Aug 18 09:31:28 Samba Server: daemon is started
Aug 18 09:31:28 miniupnpd[31824]: version 1.9 started
Aug 18 09:31:28 miniupnpd[31824]: HTTP listening on port 47369
Aug 18 09:31:28 miniupnpd[31824]: Listening for NAT-PMP/PCP traffic on port 5351
Aug 18 09:31:28 avahi-daemon[31812]: Alias name "RT-AC68P" successfully established.
Final troubleshooting in next post.