check what "/sys resource usb print detail" shows.
you should see something like this:
[admin@router3] > /system reso usb print detail
0 device="1:1" vendor="Linux 3.3.5 ehci_hcd" name="RB400 EHCI" serial-number="rb400_usb" vendor-id="0x1d6b" device-id="0x0002" speed="480 Mbps" ports=1
usb-version="2.00"
1 device="1:2" vendor="MikroTik" name="R11e-LTE" serial-number="000000000000" vendor-id="0x2cd2" device-id="0x0001" speed="480 Mbps" ports=0 usb-version="2.00"
if you already opened the device, try to unscrew and reseat the modem.