Is the module completely screwed into the rack? You may get intermittent power/signal if it is not totally screwed in, or in a test jig like the 500EXT.
Check your routing. Connect the cables you were running to your 500-series module together to confirm that your routing and cables are correct. For example, if you were using the module as an insert between output 3 and input 3, connect the XLR from output 3 directly to the XLR going to input 3.
Test your 500-series rack. If you have another, known-working 500-series module, test it in the same slot of your rack where the DIYRE module was not working.
Check Component Positions
Are all resistors in the correct positions? Check the color bands of every resistor against the sorting sheet. Pay especially close attention to those that start with the same number, for example 4.7k and 47k.
Are all ICs in the correct position and orientation?
Are all capacitors in the correction positions and orientation?