Thanks for this.

I did a dummy booking based on the itinerary in your pic. I can duplicate it, and I can see the different fare classes. I had assumed that one of these issues could have been the difference:
- your starting point is PVG. My starting point is TPE.
- you are using the China Cathay website? I am using the Hong Kong or Taiwan website.

So, I went onto the China Cathay site, and tried my booking, and the same result as before....only loaded me with the lowest, and most restrictive, fare. No other fare choices at all.

Just for ref:
11 Jan TPE - HKG
23 Jan HKG - SHA
26 Jan PVG - HKG
03 Apr HKG - TPE

returned the only fare of TWD 13,801.- (restrictive, with change fees, etc.).

Then, I noticed that your itinerary had HKG as a transit point, and not stopover. So, as soon as I changed one of my legs (for example, to TPE-xHKG-SHA) to use HKG as a transit point and still as a stopover on the return, then indeed, I can see all the Econ, Premium Econ, and Business fare classes and prices.

So, maybe the issue is that the booking engine will only show the lowest, and most restrictive fare class, if HKG is used as a stopover on both ways.

Anyway, I solved my issue by using LINE chat (very quick and responsive) to request the agent to make the booking for my desired itinerary and flexible fare class. Then, she emailed me a pay link to pay for the ticket.