EMF fluctuations in a negative reactance ring

[Sredni]

I promise I am not trying to revive a dead horse (read on and it will be clear why it is not so) but I am posting in this part of the forum for good measure.
Back in the good old days of the Kirchhoff vs Faraday rap battle, someone suggested I tried to analyze a Lewin ring (two resistors in a loop that encircles a region of variable magnetic field) that employed capacitors instead of resistors. Well, about a year ago I did just that and also made a video that showed results in accordance to what was predicted (and yes, the Kirchhoff party would interpreted in their own way, while the Faraday party would insist it's the other way around, so let's accept that and not go down that road again). Here's my old video:

https://youtu.be/qTzqIYrc_Hs


Yeah, despite my charismatic scenic presence, the perfectly timed script, along with my utter mastering of the English language and uncanny fluent British pronunciation, audio and video quality is close to zero. So I thought I might remake the video and possibly switch from mains frequency to the variable frequency of the function generator to show that, within the limits of the frequency response of the toroidal core, the theory (that keeps Ohm's law - in its generalized form - alive in all parts of the ring, but does away with KVL) held.

And indeed, everything seemed to work nice, but today when I was preparing to record the video, I've noticed that when I raise the frequency above a few tens kHz (but still under 100 kHz), I get appreciable, seemingly random, fluctuations in the electromagnetic force.
I therefore put the remake on the back burner, and I am now going to make a dedicated video to document these flukes (I am not sure I know how to do a live on YouTube to get instant feedback, maybe I'm not even allowed) and I will try to put it online in a few minutes to get direct feedback.
I am wondering if there is some theoretical reason for the EMF fluctuations I am seeing and if you have suggestions on how to perform the measurements in order to identify the problem.

BRB with the new video.

[Sredni]

Here

https://youtu.be/Y2C9NxfXqLM?si=2QQxX9mES_31YIHr