could well be a problem with fresnel zone as posted above. Mounting antenna higher could help in that case. I would check the cables (on both sides, because if it's hardware, problem might be at Side B, if it's reflection or noise, problem would possibly be near side A)
It could be the sending part of side B as you could receive a good signal there from side A, which tells that side A is sending properly. Scanning from side A the signal from side B is very weak, which means either much less sending power from side B or something in fresnel zone is disturbing your signal a lot (Maybe a rooftop made of metal (perhaps not far from your AP), where signal is reflected, may be a mountain side or similar).
The odds of getting two bad R52h out of four and mounting both bad cards in the same RB are very remote, but not impossible.
1. Check cable and antenna, if you have available, replace with others. Else you could take all your kit from side A and carry it to side B, and vice versa. If the problem occurs on other side after switching the equipment, you have to nail it down to the part of hardware, that's failing (Antenna, cable, card, RB or power supply) If the problem persists at the old location with the swapped hardware, You will know it's an environmental problem like reflection or similar. I would think if it's just noise, you would have a better signal, but very high noise levels (-90 or more), so from my point of view noise is not causing this (If anybody has other experience, please feel free to correct me on this one)