Strange, strange.
On my flight from Hawaii to Lihue (Kaua’i) the Fenix had clearly a top of descent visible on both flight plan and arc display.
But she just did not start to sink, and stayed an 10.000 feet Altitude instead.
Arrow up and arrow down for managed altitude did not change anything…
She also did not start to sink after catching the glide slope for the CATIII landing.
These were the engaged autopilot modi:
She just did not sink no matter what I tried but always stayed on the altitude I had manually set in the autopilot.
Went down to 5000 to make her catch the glideslope, but she stayed on 5000 the whole approach and just flew over the destination airport at 5000 ft.
Landed her by hand after overflying the airport without sinking…
It was not the runway, but almost… 
Can anyone please tell me what wrent wrong during this flight? Why did the manage altitude and the manage altitude during CATIII autoland absolutely not work during this flight?
What do I have to do to make her sink down to an altitude to automatically catch the glideslope? Instead of stay of example on 10.000 of 5000ft until the runway is right beneath the plane and never sinking to begin the approach?
(Start approach phase was activated in the FMC.)