Reinstall router's firmware through bootloader's menu
step-by-step instructions how to upgrade router's bootloader and firmware:
First of all please set static IP address on your network interface (e.g. 192.168.1.10)
Use private/incognito Web browsers window with cleared/disabled cache
Download latest router's bootloader and firmware version from here ( https://wiki.teltonika-networks.com/view/RUT955_Firmware_Downloads )
Power on the device while holding reset button.
Access router via web browser http://192.168.1.1/index.html
Upload new router's firmware "RUT9XX_R_00.06.xx_WEBUI.bin".
Wait few minutes.
Try to access router via web browser http://192.168.1.1
If the problem persist try to use the bootloader: https://wiki.teltonika-networks.com/view/RUT2xx_Firmware_via_The_Bootloader_Menu