Over the past couple of days my Zwift Hub trainer has had issues with both wattage and resistance. When I begin my ride, my wattage is about 80-100 watts below my usual output (It isn’t because of my effort, I’m still riding as hard as I usually do and even tested a friends device just to be sure.) I typically average between 280-320 Watts, but since this issue started I’m only averaging around 200-220 Watts while utilizing the same effort.
Despite this being frustrating, I still stuck with my ride and about 45 minutes in I was on a slight decline gradient and the resistance just stopped working entirely. The device was allowing a maximum output of about 80 Watt’s and pedaling in the highest gear is effortless.
Both the software on my Ipad and Firmware on my device are up to date. Has anybody else experienced these issues and have any advice on how to fix it?
Seems very similar, I’ve tried the recommendations on this thread except for the “virtual gears” thing, but virtual gears isn’t even listed in my settings.
getting exactly the same issue. I thought it was a Virtual Shifting issue but it looks more like a calibration problem since I disabled Virtual shifting today and didn’t pair the Zwift Click.
I’ve had to exit multiple races and it’s getting to the point it’s unusable.
Device - PC 32gb ram, intel xeon, gtx1660, cabled network. Windows 10.
Trainer - Zwift Hub all firmware up to date
iPhone 13 - companion app. Updated. WiFi 5gps
Sensors - Zwift Click, Zwift Hub, Polar HRM all via companion app.
Region - U.K.
Here is my chart from today’s attempt at starting a Hill Climb Race Club - those power spikes are resistance coming back and then disappearing. The final loss of resistance was right after the KOM start line 
The Zwift Hub is causing erratic resistance and seems to cycle through i) Too hard - but watts appear correct, ii) No resistance - cant’ make watts iii) Too hard - but watts show very low
and here are two unlisted videos of the issue.
In the first video, I reconnect the devices and go into free ride. The resistance of the trainer fluctuates as I try to keep a stable cadence causing erratic watt reporting and making it impossible to keep stable cadence.
In the second video, I thought the trainer had stabilised and at the start of the race begin ok, but then resistance disappears so I can not produce watts and I can no longer keep up with the field. Luckily, resistance comes back when I shift gear and push very large watts to catch up.
But only here 10 and 11 are useable for the rest of the race.
Here is some additional data.
This is the Power chart from ZC
Virtual shifting was turned off.
Click was disconnected.
The cadence is negatively correlated with the power as the resistance from the hub alternated between very high and very low. - remember, no virtual shifting activated in this ride.
After reaching the KOM start banner, I went to push harder and lost all resistance. But there was a 1000w spike with 0 cadence.
I don’t think this is a hardware issue, but something to do with the auto calibration method.
I’ve never had issues until the latest update and getting them frequently now.
I was connected to the PC via companion app and the trainer had been on for 5mins.
I have an issue with the watts represented by my sensors, although what seems to be different to the posts here is that my Watt output is consistent (consistently low). I cannot seem to find the auto gears and auto calibration information. (I’m new here). So currently haven’t tested a way of fixing it.
The only reason I think my Watts is showing low on Zwift is that on Rouvy my Watts are more than double anything recorded here on Zwift, again consistent. The watts here on Zwift and Rouvy don’t spike or drop to zero.
The difference that is probable from the posts here is that i don’t use a smart trainer only cheap sensors attached to my bike.
Hi Steve
Did you find a solution? My son is experiencing the same on his Zwift Hub.
Best regards
Jens
Hi Jens
Yep, I reached out to Zwift support and sent them a description of what was happening plus some videos and screenshots.
They swapped out the trainer which resolved it. Now they are investigating the old trainer to see what has happened.
Hi Steve, thank you very much! We are in a dialogue with Zwift Support, so hopefully we can work it out.
Best regards
Jens
Great!. definitely share the screenshots with them. Mine show that I would get power for a few seconds then lose it. I would do a spin-down and get a large power spike and then the power would come back for a little longer.
I started doing reboots between the spin downs and after around 7 or 8 reboots the trainer would hold power for the duration of the session.
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