Actually, it’s also worth noting that it looks like your weight dropped slightly and that could be playing a role in the calculations. You are so close to the A/B line that it doesn’t take much to tip you either way.
David from Zwift did emphatically say earlier that 1-3 minute power does not count for zFTP. But Paul’s drop of 5 watts for his zFTP while increasing his 3 minute power by 34 watts and his 5 minute power by only 2 watts would suggest that power above 3 minutes is part of the calculation of zFTP.
Yes I try and ensure my weight is accurate, so it might play a role. I’m always between 60 & 62kg, but as you say I’m so close to the limit. I’ve actually enjoyed racing Cat A, I’m struggling to finish in the top 50%, but it makes a change from feeling fairly comfortable for a lot of the race, then getting ripped apart by the guys in Cat B that can put out huge watts in the sprints or climbs that only last a couple of minutes.