You may think you installed that version, but your router says otherwise (and it's always right). Yes, there may be a bug in this specific firmware, but I would guess someone before you would have discovered this many weeks ago by now.
Do you have a USB drive connected to the router? If so, Safely remove it via the GUI, physically remove it, then do a reboot of the router. Then attempt to flash the firmware you're indicating in your post above. After verifying that the correct version is installed, insert the USB drive again, then reboot the system once more.
Btw, I would not be using a phone to do this with.