I made this comment back in Feb pretty much showing how sensitive one type of CP calculation was to changes in 3 min power - Category Enforcement - How is my category calculated? [February 2022] - #603 by Edward_Bowen
The rider in the other thread didn’t post his power curve, but we also don’t know exactly how zwift is calculating the zFTP, so the only thing to say is to get power bests at different times starting at 3 min upwards and the CP should be calculated reasonably.