Aperture Priority does not guarantee identical results frame to frame; it only meters each shot and chooses what it thinks is the best matching shutter speed.

A few things explain your result:

1. The framing changed slightly. Your photos contain different amounts of bright sky and darker foreground. That changes the meter reading, especially in a high-contrast scene.
2. The settings are not exact stop-for-stop matches. Your first exposure is about half a stop brighter than the others, so the camera did not choose mathematically identical exposure values.
3. Meters and camera settings are approximate. The “correct” shutter speed may fall between available settings, and the camera rounds to the nearest value.

So the camera was reacting to both the scene content and normal metering/rounding limits.

If you want to test exposure consistency, use a tripod, keep the composition identical, and shoot a static subject in stable light (indoors is even better). Very bright skies plus dark foregrounds are difficult scenes for any meter.