The pins on the seven segment LCD front panel display (DS1) may not protrude through to the rear side of the board. This is OK. The LED Backlight Diffuser should be mounted flush against its small spacers (2 per side.) Also the LCD display should be mounted flush with the LED Backlight Diffuser.
We recommend soldering these pins on the front side of the PCB if you are nervous about doing it from the rear. The PCB holes are plated through and will make a good connection even if you solder from the front.
If you get intermittent lighting of segments on the display, check the solder connections for the LCD display again. Also check to see that the LCD driver chip, U1 on the rear of the FP board, is fully inserted in its socket. (Remove U1 and re-insert it.) Check for pins that may have folded over on U1 when it was inserted. Also check to see that the socket pins are soldered properly.