The cause is apparent! The connectors on the cables are wrong!
Currently only 50% of the pin length goes into the connector!
(Koji, Jenne, Yuta)
We found one of DAC cables had a poor contact.
That probably caused our too much "tilt" of the beam into MC.
It was because one of the DAC cables(labeled CAB_1Y4_88) had a poor contact.
If I push it really hard, it is ok. But maybe we'd better replace the cable.
What caused a poor connection?:
I don't know.
A month ago, we checked that they are connected, but things change.