That’s helpful information there! I can see that you were on firmware version 1.3.17 earlier in the day on March 5. Since you updated to 1.5.36 later that day, I’m assuming this was after you contacted Zwift Support and were advised to update. I’ll share this detail with our team.
Correct. The error existed prior to March 5th and the Wahoo firmware update was a troubleshooting step.
I’ve the exact same problem as you’ve described on this topic. I’ve been in touch with the support multiple times, but no real solution has been provided yet. Hope they sort it out soon 
Hi all,
After doing a lot of troubleshooting and some frustrating moments. I was able to fix it (for now).
So I was searching various topics and found an old topic (2022) where someone mentioned a wrong wheel-size in the Wahoo fitness app had impact on the resistance in Zwift. This person said everything worked well after resetting the wheel size.
I’ve thought to give it a go and did the same thing:
- Reinstalled the Wahoo app
- Added the Kickr Core
- Went to the settings
- Changed the wheel size from the default (700 18C) to 700 x 19C
- Performed a spindown
After these steps, I opened Zwift and connected the Kickr Core and Zwift Play… and everything worked as expected on my tablet.
I will try to use Zwift on my laptop later today to see if it works on my other devices.
Well I’ll be darned, we finally have a workaround!
All I did from the instructions was change the wheel size. No reinstall or spindown.
Booted up zwift, and gear shifting did change resistance.
I tried @Will_Rsnhk’s steps without reinstalling and repairing the Kickr Core and I can confirm that I can now experience resistance changes as well!
BUT everything below gear 8 felt almost the same. As I just bought my Zwift setup and I haven’t had the chance to experience virtual shifting before, I am unsure if it’s the normal behavior or just half the way of a fix.
Anyway thanks @Will_Rsnhk for sharing! 
@Markus_Pro Great to read this fix also has a positive effect on your setup.
Have you tried something with a steep climb? Because I can imagine if you tried to ride on a flat route, everything below 8 feels too light.
Maybe try ‘The Grade’ segment in the route Elevation Evaluation to see how your Zwift setup performs on a climb.
You are my Zwift hero
Worked for me. What a stupid issue.
Thank you
@Will_Rsnhk, ok I will try again with gradient. Did anyone test what happens with the other wheel sizes? Does it matter which wheel size you use (obviously yes, but I mean beside 700 18C)?
@Olivier_Mesa: Indeed, it’s a bit stupid, but good to have an easy fix
That’s incredible !!! I have put my 700x40 set up back from the 700x18, then spindown… And now work it !!!
What a bullshit 
You are our angel !!!
Ok, I will answer my questions by myself. I tried some course with gradient and indeed gears lower 8 grade are effective there. So I guess it’s the normal behaviour, even so I didn’t expect it to behave like that, but it’s ok, it works.
I also discovered that it does not matter which wheel size you use once you changed it one time. So after my second try I changed it to some other value, but it was the same feeling. I also changed it back to 700 18C and it still worked. So you might need to change the wheel size for once.
I will wait one or two more days for more feedback and will then mark our hero @Will_Rsnhk’s answer as solution.
@Zwift support I guess Will earns some free month of Zwift. 
I can’t believe it, it actually worked. I also just changed the wheel size, and that was enough.
Personally, I had only contacted Zwift technical support, thinking that the problem came from there, but if anyone was also in contact with Wahoo, it might be a good idea to let them know the solution to the problem. In the end, the problem came more from their equipment, but for some unknown reason…
Hi @Will_Rsnhk
Thanks for sharing your workaround. I’ve marked this a “solution” for now until we can get this resolved properly.
Hello,
After the latest zwift update, the issue is back again. No resistance whatsoever even at high gears. I haven’t tried the workaround once again, will do but the issue is not resolved
Regards
Hi @Andrea_Piscopo_FITRI. Thanks for your findings and for keeping us posted! This is Jose from Zwift.
Andrea, we would appreciate it if you could let us know how things are going after trying the workaround, as it would greatly help us document and review it with our team. We appreciate your support.
I had this issue pop up for me yesterday. Changing the wheel size on the wahoo app resolved it. Much appreciation to the poster who put up this solution. Thank you.
Ok before opening zwift i went to the wahoo app, changed wheel circumference size, killed wahoo app and I got resistance back on the trainer on zwift
Hello I am using a Wahoo Kickr Core Trainer and after that update the resistance keeps shifting more than it did before that update. I dont know if the update contained any software updates but it seems a bit odd that it suddenly changed the feedback and resistance from the Kickr Core after that update. I am aslo using Zwift play controllers but Im not using virtual shifting, I don`t know if that has something to do with it. I will investigate further on this because it felt like I had virtual shifting on in a way, it was the same feeling in resistance from the Kickr Core when you are using virtual shifting.
I hope someone can help me a bit here, cause I really like Zwift and have used it for years and will continue to use Zwift many years to come
I will reply on my own question, I tested it now. First without turning on Zwift play Controllers and rode 10km without any sudden resistance drop or resistance hardened issues. Stopped and turned on Controllers and it was the same as before earlier today without sudden resistance drop or resistance hardened. So if it was a one time bug and all is back to normal I am okay with that 