Constantly undulating power reading when riding steady

My wife is having a weird issue with Zwift where the power reading is cycling up and down continually in a regular pattern despite riding at a steady effort. The pattern appears to repeat about every 9-10 crank revolutions and power varies by 45-60 watts from the peak to the valley. The overall average power reading changes with her effort level, but the undulating power pattern continues regardless of effort. Overall average power seems plausible despite the fluctuations but we haven’t tested with a separate power meter to check. Setup is Apple TV 4K Gen 2, using Zwift Click V1, and a Wahoo Kickr Core v6. I don’t have the same problem on the same trainer, but I use a crank power meter as the power source, she is using the trainer as the power source. She is having the same problem regardless of whether she connects directly to the trainer using Bluetooth, or whether she connects via her phone.

Any ideas?

Pic attached to illustrate the issue while riding on a flat route. She does ride a very slow cadence of about 70 rpm average but as I mentioned the pattern repeats about every 9-10 rpms.

Is the gear ratio on her bike within spec according to this guide?

https://support.wahoofitness.com/hc/en-us/articles/16865097915666-Zwift-virtual-shifting-with-Wahoo-smart-trainers

Could this be the 10Hz “race mode” power variation?

Looks more like this, or a Bluetooth problem with whatever the game is running on

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Looks like she was using too low a gear. I got her to shift to the 50 and she’s on either the 17 or 19, not sure which as she’s still riding, and that seems to have fixed the problem. Thanks!!!

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