Even if the modules are the same model, they could have slightly different requirements for the strength of the received X10 signal on the power line. Manufacturing tolerances and variations in the parts and design over the years can affect this. I suspect that the X10 signal getting to both modules is weaker than before and one is failing to receive it before the other does.
At this point, I would plug in my trusty XTBM-Pro signal meter and start checking out the circuit. If you don't have a signal meter, try to think of anything that may have been plugged into an outlet recently, unplug it, and retest. You can also go to your breaker panel and turn off all circuits other than the one your WS467 modules are on. If the problem goes away, turn breakers back on one at a time, retesting each time, until the problem returns, then continue to narrow it down from there. Keep in mind that the potentially offending device is not necessarily plugged into an outlet; it could even be a light bulb. And it may be more than one device causing the problem; noise and signal blocking generated by each bad device is cumulative and X10 devices will begin to stop responding once you cross a threshold. (This really is a lot easier with a meter!) The devices on the same circuit branch (same breaker) with the WS467s are more likely to affect them.