shd9 is correct. Whilst you can see the fare rules on ITA Matrix, you can’t see the routing restrictions.

For CX fares from PVG-SIN, you can route PVG-HKG-SIN or PVG-HKG-BKK-SIN on CX flights only. From PVG-MNL, it’s only PVG-HKG-MNL.

You can book PVG-HKG-SIN/MNL-HKG-PVG as an open jaw and combine half round trips of each respective fare together.