Similar issue for me. Bought the DUO in June 2020 and yesterday 3 April 2022 started to notice strange behavior. I have a 3-seconds avg power field on my garmin edge 830 and it was fluctuating up and down too much. It started to continuously fluctuate with about 100w difference between min and max values while I was on a flat stretch doing consistent effort.
I haven’t tried anything yet to resolve the issue like recalibration etc but did just contact support. I’ll see what they come up with.
It maybe isn’t related but my Favero Be Pro S was consistent for 3 or 4 years and then it became erratic. I figured out what it was though, I had a bike fit and it had put me in a marginally different position and I was now on occasions touching the pod with the cleat. I subsequently trimmed the cleat slightly with a blade and they’ve been consistent again for the last 2 years.
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I’m also seeing odd behavior. I’m suspecting temperature compensation might explain some of it, as noted by @kevistraining above, because I often calibrate after taking the bike out in the cold, or vice versa.
I’ve had my Uno replaced before, but that was due to a constant underestimating of 40 W. This time it’s different.
Yesterday, I tested the pedals against my Tacx Neo. Before the ride I calibrated the pedal using the Favero app. The bike was mounted upright on the trainer, the cranks where oriented vertically, and I was not touching the bike. When I started the ride the pedal was reporting 150 W when resistance was very low and the Tacx reported less than 100 W. I stopped and did another calibration in exactly the same way as before, and after that the pedal reported correct data.
You can see the power data here: https://zwiftpower.com/analysis.php?set_id=240397
On March 23, I climbed a hill, and the pedal reported an average of 293 W for 32 minutes. This is more than I have ever managed, and I’m not even in my best shape yet. Two years ago I did the same climb more than 4 minutes faster at just 286 W. According to bikecalculator.com I would need to be 17 kg heavier to explain the 4 minute difference, and I’m not. Even if I could have done 293 W, my heart rate would have been much higher. After 18 minutes it had not exceeded 170 bpm. When I did intervals at 280 W yesterday, my HR reached 177 within 7 minutes.
You can see that ride here: https://www.strava.com/activities/6870478921
On February 28 I suspected something was wrong. I had already stopped and calibrated several times. On a flat stretch I pedaled slowly at 8 km/h for 45 seconds. Then I returned, re-calibrated, and did it again. The first time I averaged 106 W, and the second time 68 W.
UPDATE: I did another test today, 90 minutes indoors with a steady temperature. I calibrated the pedals before the workout, as well as every 10-15 minutes. The pedals tracked the Neo well all the time, except for after the very last calibration.
Between 1:11:00 and 1:15:00 the difference in average power was a half percent. Between 1:18:00 and 1:22:00 the difference was more than 4%.
All the data is available at ZwiftPower - Login
Ugh, not even sure where to start. Mine are out of warranty now, and they’ve started to show L/R balance that heavily favors the L (60/40ish), which tends to translate to lower power than I’d expect. I’ve been back and forth with their support and done the static weight test. A few times they’ve said there were “strange” readings from the right, but they couldn’t point to anything. I’m a little stumped about what to do now.
Hey Wirt, where you able to fix this somehow? Having the same issues with my Faveros - ofcourse they are also outside of warranty… Pretty frustrating.
Maybe completely unrelated but I found my older Favero Be Pro S went erratic when I changed to the Keo cleats. After a bit I realised what it was, they were skiffing the pod so I had to marginally trim them down.
Honestly, I’m pretty embarrassed to admit but I was wrong. The second unit was seemingly even for a bit (or it was placebo) then started showing same kind of discrepancy as the first pair.
I chalked it up to bad batch and moved on. My power2max (right only obviously) was showing exactly double my right favero so I assumed favero was just wrong on the left.
Then couple months ago I kept having lower back pains like I never experienced before. Riding was helping but whenever I sat on the computer it’d come back. I’ve visited sports massage therapists and chiropractor’s and guess what… My left side was indeed a little f’ed up. Not by much but definitely weaker. It was pretty surprising to see since I’m left side dominant but somehow my setup at home, posture, bad habits are I guess contributing to this.
Back pain etc gone and I’m paying more attention nowadays but unfortunately don’t have the faveros or other dual sided pm’s to test at the moment.
Thanks for reminding me to post a resolve.
TLDR: I’m dumb.
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Just to give an alternate view. I ordered my Assioma’s in July 2019 and they’ve been pretty much flawless ever since.
I’ve run them over 5 bikes swapping multiple times per week, and still good.
Even survived getting hit by a car, and still match up with a Power2Max on my gravel bike
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@fluffelz
Here’s another follow up!
After seeing @GPLama’s review of the 9200 and 8100 Stages and have been wanting to slap a power meter on my latest bike build, so I pulled trigger on a dual sided Stages 9200. Just arrived yesterday and I rode it today for the first time. This isn’t to show you accuracy or anything but just as proof of how uneven I am as mentioned in my previous post. 2 Assiomas and now Stages agree that my left is stronger than my right (sorry I got mixed up last time I posted. My dominant is indeed left and is higher power as seen below for both assiomas and Stages)
Too bad I don’t have the Assiomas anymore to test head to head with Stages but I’m satisfied.
Now, how I solve this imbalance is a separate issue 
Physical therapy? ugh…
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I’m trying to solve a 40:60 imbalance myself too (which had steadily grown from September 2020 when I got my assiomas from 46:54 (so quite acceptable) to 40:60 (way too high) by January 2022). Some things that might have contributed: slightly oneven setup of the handlebar and hoods and cleats (check that they are mirror imaged) and a saddle slightly too high
Not exactly what I was hoping to hear. But it also makes sense in relation to my own problem. After an accident in 2020 and more intensive physiotherapy, my L/R balance had obviously improved in the process. Due to “lack of time” since returning to normal work, it has now obviously deteriorated so much that I almost hoped it was an assiomas problem.
Thus also an approach for you. Core & stability exercises!
These have obviously helped me in the past.
To be honest I wouldn’t completely dismiss your findings either. If you ever get a chance, compare it to other power meters! Faulty units exist out there, I have no doubt.