Update:

1) Taiwan immigration did not ask to see return ticket at all.

2) CX's machine gave a red light when scanning BPs at the gate - it was kind of comic - the woman before us, got a red light with a Canadian passport and a BP looked like from Kiosk. Our online BPs also got a red light. The gentleman followed us with a Canadian passport also got a red light.

The GA asked for help and another CX GA running back and forth with the passports ant the return tickets to the nearby service counter where they looked up the visa requirements...

I found this procedure of CX should be performed at the counter outside security - their system should NOT allowed OCLI or Kiosk check in if Visa check is necessary. Just display a message "Please check in with airport agent." so any Visa check is performed and taken care of long before boarding.