The a/c that was due to operate the cancelled flight earlier in the week is exactly the same one that is down for tonights trip, but checking there is nothing wrong with it as it has just arrived in ORD from NRT. The loads showing look healthy enough. No idea what they are doing.
However is the rest of the B787 fleet operating normally. It's likely one is not and MAN is that bit "easier" to cancel when you have such an operation to other hubs and the other airport down south!
I will say that it's very unprofessional to have two cancellations within a week considering they should at least be able to find a B752 or B763 to fill if it's a B788 issue.