It makes no sense for the LED to be dim. LED can only be ON at the designed brightness or OFF since LED is powered through a resistor from a fixed 5V supply and if the supply is not 5V then LED will not be allowed to be ON.
Is the DSSR20 installed inside or outside ? any chance water or condensation got to it ?
Maybe is because of the litign and angle the photo is made at but take a closer look at the two 5.1kOhm resistors that are connected in series (they are in the opposite corner of where the LED is) and they just look like both are soldered on only one side but may be just the shade and light from the photo. They power the entire circuit so if one of them is not soldered or makes just intermittent contact that may also be the problem.
During production I only see the LED that may not solder properly for less than 1% of the boards and I need to manually correct that but never seen any of the resistors not soldered properly before so maybe is just shade.
If that is not the problem I will ask you to send it to me to check in to more details and I will pay for shipping costs.