[Valera / Kiwamu]
It was because of a loose connection. Pushing the connector solved the issue.
We really have to think about making reliable connections and strain reliefs.
Yesterday we found that MC3 OSEM LL PD did not have a sensible signal - the readback was close to zero and it was making MC move around. I disabled the PD LL so that the damping is done with just three face plus side PDs. There still no signal from MC3 LL PD today. It needs debugging.