Hi again,
Ok. There has to be something fairly simple wrong here, most likely in the wiring or one or more of the connections or the signal. The reason it must be simple is because the circuit looks completely symmetrical and since it works in one 'direction' it should work in the other exactly the same way except different transistors are turned on. There could even be a transistor burnt out now.
So what you would have to do is make some measurements. First, make sure your signals are the same for both forward and reverse. Make sure the levels getting to the transistors are the same either way.
Next, measure the voltage across each transistor Drain to Source and see that when it is supposed to be turned 'on' that it actually shows a low voltage drop across D to S. Make sure that when it is not supposed to be 'on' that it shows a higher voltage D to S.
You should be able to quickly find the problem that way. Once you find a problem, try to find out what is causing that. It may take a little work to troubleshoot though because so many MOSFETs are in parallel. Because of that, you may have to open up the gate lead (maybe remove a resistor) and tie the gate either to plus or to ground to turn the MOSFET off, and if you do that with 3 out of 4 that are in parallel then you can check each individual MOSFET to see that it works as it should. The one that isnt tied high (or low) should turn on and off with the drive signal with no problem. Once all 4 in that section are working the whole circuit should work as planned.