This is probably the most serious overbook I have ever seen.

I was returning from Seoul in Y. There was an a/c change from a 343 to a 33B. 343 has 30 J seats or 38 J+F seats. 33B has 41 J seats. There were still three J passengers (as I was told by one of them) that could not be accommodated. So the flight was oversold by 6 to 14 passengers, depending on what 343 was originally planned. They were probably out of the old 44-seat 33A (?).

The result:
* One or two upset passengers.
* Rearranging Y passengers to accommodate the downgraded J passengers.
* Busy crew. The ISM was personally serving one of the downgraded passengers, bring in things from the J section. A senior FA greeted a few passengers (not me though - the second or third time ever since I was a DM). I am not complaining - the crew is under a lot of stress.

I spoke with one of the downgraded passengers. He traveled often enough that he knew these things happen and someone had to concede. He did not want the crew to feel worse than they already did.

What kind of compensation did downgraded J pax receive?

I have seen LHR operations offering GBP 970 for J to Y downgrades.

I did not ask. It is a regional sector. I don't think the compensation is too high. (However, GBP970 for a one sector downgrade for LHR is really low.)

I would have thought CX would offer them a J seat on a later flight with some cash compensation. Was yours the last flight out?

No, there was one more flight at night. That was yesterday (Friday) and things were chaotic. There were transit passengers who had to catch night flights out who could not wait for the last flight.