I have all the buttons showing up, but a different problem with the same outcome. Trying to check-in for CX 888:
"Due to certain flight restrictions, Online Check-In is unavailable. Please proceed to the airport for Check-In. We apologise for the inconvenience."
Sounds like a bug. Some airports are so archaic that you can't do OLCI in advance (like Ningbo to HKG), but CX 888 shouldn't have this problem.