I understand the frustration.
But your flight is only in ten days.
Apparently all morning flights TPE-HKG on 22/4 are fully booked (availability in J and Y are zeroed on EF).
Hence an agent cannot find you a seat on those flights and you need Head office has to unblock a seat for you. These manual interventions might not been done within minutes but when the system reviews the situation, and 10 days ahead there is no urgency.
Glad it ends well but CX is a very reliable airline for those flight schedule changes.