Fusion in Resolve - zooming keyframe timeline

Is there any logic as to where the zoom slide is zooming too? it feels like it's zooming to playhead, until it snaps to a random spot and the the scale goes like 10x from where it was at.

I can't figure out how to consistently zoom into my keyframes.

I just use zoom to fit button in the top corner of the keyframe editor if that is what you mean. Otherwise I move about by scrolling with mouse wheel for zoom. Where mouse is pointed when I scroll it zooms. And middle mouse button turns cursor in the hand so I cam move that way. No issues. If you have lost your place, use zoom to fit command. Other options in the three dot menu allows you to quickly tidy up the number of displayed frames, parameters, tools etc. If you are comfortable with it, its super easy and efficient to move about. There are tones of customization available of many differnt UI elements and ways keyframes are displayed, so you should be able to find method that works for you. Spline editor also mirrors the keyframe editor to the extent they overlap and can both be displayed at the same time for greater level of control.

Is there any logic as to where the zoom slide is zooming too? it feels like it's zooming to playhead, until it snaps to a random spot and the the scale goes like 10x from where it was at.

You zoom (or, at least, I zoom) by clicking on the header that shows the frame numbers and then dragging left or right. Left "zooms out" and shows a larger range, right "zooms in" and shows a smaller range which makes it easier to select things from individual frames.

The center of the zoom range is based on where you press down on the mouse button before starting to drag it. So if you click on the "500" that marks frame 500 and then drag right, frame 500 will remain in the same place while the frames left and right of it will expand outwards.

Therefore, if what you want to do is zoom in on frame 700 in order to select individual keyframes in that neighborhood, then click on the "700" and drag right. If the "700" is very close to the right edge of the screen, you might want to click between it and the right edge before dragging right, as that will tend to move it closer to the center.