Bought a TRB255 secondhand and needed to factory reset it, since no information on the previous configuration was present.
Holding reset will after 4 sec do a reboot (both connection status and signal strenght LED’s flash) but holding longer will not do anything more. Signal strenght LEDs will not do a countdown.
The device will stay indefinitely in a state where all status LED’s blink together slowly and all signal strenght leds blink together slowly. Status group LEDs and signal strenght group LED not simultaneously.
Maybe you put the device in boot loader mode.
The bootloader menu is a special gateway state used as a recovery tool in case the gateway becomes inaccessible even after a factory reset. It can be used to upgrade the gateway’s firmware or bootloader version. https://wiki.teltonika-networks.com/view/TRB255_Device_Recovery_Options