USB flash not recognized in /dev/

When i connect USB flash to board, sometimes it doesn’t show in /dev/ .
dmesg output:

[   19.398984] USB QCMAP NL IOCTL Snd GETNEIGH Succ
[   19.415355] QCMAP:Start Main
[   19.453920] USB QCMAP NL IOCTL Snd GETNEIGH Succ
[   19.545707] QCMAP:Start DHCP server
[   19.557725] QCMAP:DHCP server started
[   19.806623] QCMAP:Init Complete
[   19.851113] USB QCMAP NL IOCTL Snd GETNEIGH Succ
[   23.397277] sps:BAM 0x04044000 is registered.
[   23.397544] sps:BAM 0x04044000 (va:0xd1820000) enabled: ver:0x27, number of pipes:6
[   24.181201] PSM: DMS Ind register  - result: 0, error: 0
[   24.181909] PSM: Oprt mode event report req qmi response - result: 0, error: 0
[   24.182532] PSM: result - 0 error - 0
[   24.182584] PSM: Modem oprt mode - 0
[   24.183799] PSM: backup_nv_path /data/psm/psm_nv_backup.txt
[   24.187264] PSM: Supported: 0
[   24.187334] PSM: Log and QMI Init completed
[   24.187374] PSM: Supported: 0
[   24.187623] PSM: Core server init completed
[   24.187964] PSM: Client and event thread created
[   24.827999] gpio_check_and_wake: wake-n_gpio26 STATE=WAKEUP
[   24.833475] swimcu_calibrate_event_handle: MCU calibrate completed with remaining time 0
[   24.833500] swimcu_lpo_calibrate_calc: MCU time=25000 vs MDM time=24402 
[   24.833518] gpio_check_and_wake: wake-n_gpio26 STATE=SLEEP
[   31.581249] usb 1-1: device descriptor read/64, error -110
[   31.811255] usb 1-1: new high-speed USB device number 3 using msm_hsic_host
[   46.991241] usb 1-1: device descriptor read/64, error -110
[   62.281241] usb 1-1: device descriptor read/64, error -110
[   62.511251] usb 1-1: new high-speed USB device number 4 using msm_hsic_host
[   72.971251] usb 1-1: device not accepting address 4, error -110
[   73.090779] usb 1-1: new high-speed USB device number 5 using msm_hsic_host
[   83.551236] usb 1-1: device not accepting address 5, error -110
[   83.551479] usb usb1-port1: unable to enumerate USB device
[   83.552259] msm_hsic_host 7c00000.hsic_host: HSIC-USB in low power mode
[  110.736727] sh (1643) used greatest stack depth: 4468 bytes left
[  121.121195] sierra_startup_monitor

Also it isn’t recognized after I type reboot , but when I power off my board and power it back on it is recognized and shown as /dev/sda1.
Anybody has any idea why?
Thanks