It sounds like a manufacturing issue to me, so I don't think so. The batch they ordered could have been faulty, but I'm assuming that ESA uses samples taken from multiple runs to minimize failures, so that's fairly unlikely.
It could be a design issue too. Like are they accidentally over-voltaging the clock with a transient or some sort of power sequencing issue? Or does some component have tin somewhere? Really hard to say at this point.
Tin forms whiskers, small hairlike growths on the metal that can cause short circuits. We've already lost a satellite to this phenomenon, although I would hope it's not a problem anymore with current metallurgical techniques
If I remember right, tin whiskers were determined to be the cause in the crazy Toyota runaway accelerator pedals a few years back. I think it's mainly an issue with lead-free solders, which RoHS has forced into widespread usage over the last decade.
The problem was ultimately found to be a combination of pedals being pressed by floor mats, pedals sticking on their own, and drivers pressing the wrong pedal.
ESA is not part of the EU -- it's an international organization, and is exempt from national law in the same way as an embassy. Even if RoHS applies to spacecraft, it probably doesn't apply to ESA's spacecraft.
That's not to say acquiring non-RoHS components isn't made more difficult by RoHS.
