Current fluctuations with steady throttle

Hello, I came across some weird numbers and am trying to figure out what's going on.

Bixler 3, with a vanilla latest Arduplane (V3.3.0, no airframe specific tuning params) flying mostly RTL and Guided on a windy day.

No airspeed sensor, so GPS is only source of speed data.

Most of the flight was flying circles with a really long (in time) upwind leg and a really short downwind leg.

I initially plotted current (CURR -> Curr) and saw a periodic signal. I expected this to coincide with the upwind leg (low ground speed), as the autopilot would see a reduced (ground)speed and would probably try to compensate.

To verify this, I also plotted GPS speed (GPS -> Spd), only to find out that high ground speed and high current went hand in hand (if anything, the current seems to lead the speed a little), which is exactly the opposite of what I was expecting.

Finally, I plotted throttle (CURR -> Throttle). Apart from a bit at the start and finish (manual take off and landing), the throttle seems fixed.

Here is a picture of the whole data.

3691228968?profile=original

and here a zoomed area:

3691228989?profile=original

I can't attach the dataflash due to max size of 7Mb (.log is 42 and .bin is 18).

So, my question is, since throttle appears fixed and presumably, airspeed must have been more or less constant, what might be causing this current fluctuation?

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