Same problem for me, since start of the year. As the gradient changes the resistance does not change. Riding up a 10% hill and it’s as easy as 0%. Takes the enjoyment out of the courses. Please fix Zwift, especially now we are doing tour.
Double check that you are running the latest version of Zwift. Do not depend on auto-update. Manually force an update check if you are using Apple TV, iPhone, or Android phones. Macbooks auto update when you start so that shouldn’t be an issue. Windows, I’m not so sure but double check.
Check to see that your trainer firmware is the latest and greatest.
Make sure you have everything paired correctly. Pairing power from your trainer is not the same as pairing your trainer as the “Controllable Trainer”. The “Controllable Trainer” is what provides the resistance feedback when the road gradient changes in Zwift. Note: If doing a Zwift workout, the gradient changes are irrelevant since the trainer will be in ERG mode.
When pairing the “Controllable Trainer” or “Power”, if you have more than one option for the same trainer and one is an FE-C option, then use teh FE-C option.
If you’re using ANT+ and a computer, you might consider a USB extension cable to get the dongle closer to your trainer.
Whether, Bluetooth or ANT+, you might be getting signal interference from neighbor WiFi, your own WiFi, microwave ovens, etc… Hence, you might find one works better than the other. You might also consider moving your WiFi to 5GHz where it will not share spectrum w/Bluetooth and ANT+.