Motion Refuses to Zoom Vertically

I'm editing a section of keyframes in the keyframe editor, and Motion refuses to zoom any further vertically.

It worked as expected at first, but then suddenly it zoomed out and I was unable to return to its original zoom.

Here is the example: https://youtu.be/rW_gyu-Szlo

Why are the keyframes so short, that it looks like a straight line, and why can't I zoom into them?

If you look to the inspector, you will notice that the keyframes reach values of up to 300, which means the keyframes should easily be able to fit in the amount of vertical space. Am I missing a keyboard shortcut? Do I accidentally have something locked?

Please help.