Cubic Bézier easing function in timeline sometimes produces wrong values

Steps to reproduce

1. Install the attached datapack and rejoin the world. The datapack creates a timeline overriding the sun angle environment attribute.

2. Pause time: /time of overworld pause.

3. Set time to 0: /time of overworld set 0.

4. Observe that the sun is at the east. → ✅

5. Resume time: /time of overworld resume.

6. Observe the position of the sun.

Expected behavior

The sun smoothly rises from the east.

The easing function is a Cubic Bézier curve. Its control points are P1 = (0, 0.5) and P2 = (0, 0.5).
The visualization of this curve is attached.

What is happening instead

The sun flashes in the sky, and then rises from the west.