Cathay Pacific does not require medical clearance to use a CPAP, but they do require 48 hours notice prior to your flight to use one. [Source]

It's good that you have a battery pack as there have been reports of passengers being denied the use of aircraft in-seat power outlets for CPAP machines. CX has this posted on their website here.

Obviously any given crew might or might not be aware of these policies. Your prior 10-15 uses were probably with crews that weren't aware and/or didn't care about the "official" rules on CPAP.