Been having nearly the same issue, I could set them up and would connect but only at very short ranges, had the vendor replace both the Revo and the OPlink but the same again! thought I was going mad!, tried reverting the firmware and updating, then I remembered I had an Immersion RC power meter so I hooked up the Revo and got 89mw output, then I hooked up the OPlink and got 0mw, so now waiting for a third OPlink!! mine would connect but only -60DB at best so there must be a batch with duff output amp stage!
I have a batch of 3-4 that all had shorts in the antenna connection, which either prevented them from working all together or the had very limited range.
The problem is in an internal layer of the board, where there is not enough clearance between the ground plane and the antenna pin. This problem actually exists in the gerber files of the original OPLink, but apparently didn't cause a problem, probably due to different board manufacturers specs. We've discussed this with at least one of the manufacturers, and he said he fix it, but I'm sure there are still plenty of bad ones out there.
We diagnosed and fixed the problem by removing the antenna connector, drilling out the center hole with a very small drill bit to remove the short, and then soldering a wire directly to the module. Not an ideal solution, but it brought the modules back to life.