Regarding your issue could you try doing this steps:
-> Install this first
1.Turn off/unplug TRB14x;
2.Press and hold reset button, at the same time plug the power cable and keep holding reset button for about 5 seconds (mobile signal LED's should start blinking);
3.Use cd command to navigate to the place where you saved the tlt-rootfs-trb1400.ubi file (Example: cd C:\Users\ma.ju\AppData\Local\Temp);
4.Then use this command: fastboot flash rootfs_a tlt-rootfs-trb1400.ubi
5. When it completes the process use this command; fastboot flash rootfs_b build/tlt-rootfs-trb1400.ubi
6.Then use this command: fastboot flash boot_a tlt-boot-trb1400.img
7. When it completes the process use this command; fastboot flash boot_a tlt-boot-trb1400.img
8. When it is done unplug and plug your device again, it should boot up as normal
9. Install the latest software through WebUI.
UBI files can be downloaded from here: https://we.tl/t-hHJdVuG2OU
Hope it helps.