Shuji at Zwift HQ here. What changed is your FTP number. It was 210 on September 19 and was changed to 180 on September 21. It sounds like the reduction is too big of a jump for your level of fitness. To test this theory out you can manually adjust your FTP to where it was, or perhaps make a less drastic reduction?
Functional threshold power is a measure of the watts you can holder over 5 / 20 / 60 minutes depending on the FTP testing method you use, and is a proxy for your level of fitness. Many workouts in Zwift are power-based on a percentage of your FTP, and each block in a structured workout has you hit a target of X% of that FTP, which accounts for the too-easy feeling you described.
We introduced a new FTP testing method in The Grade expansion of Watopia. It’s the most fun (least awful?) method to do an FTP test. May I suggest giving a full effort in free-ride mode to determine your current level of fitness?