emphasis fails to work properly for custom series with more then 2970 data points

### Version

6.0.0

### Link to Minimal Reproduction

https://codesandbox.io/p/devbox/wizardly-hypatia-q3q2jt

### Steps to Reproduce

1. run the reproducer
2. 4 custom series charts will be displayed
--- the first chart has 3 * 100 datapoints
--- the second chart has 3 *990 datapoints
--- the third chart has 3 * 991 datapoints
--- the forth chart has 3 * 2000 datapoints
3. Mouse over the rectangles in each of the 4 charts
--- the charts will properly display a tooltip
------ good
--- the fist and second charts will also change the rectangle chart color to blue and display the name in black over the rectangle chart segment
------ good
--- the third and forth charts will only change the rectangle chart color to blue
------ bad
4. For each of the 4 charts, use the sliderto zoom in so that you can see distinct rectangles with text
5. Repeat step 3.
--- same results for the first and second charts
------ good
--- same results for the third chart
------ bad
--- the forth chart works properly
------ good ????

### Current Behavior

The first and second charts work as expected.
The third chart never works as expected.
The forth chart only works when "zoomed in? ????

### Expected Behavior

The third and forth charts should work identical to the first and second charts

### Environment

```markdown
- OS: n/a
- Browser: all browser
- Framework: javascript
```

### Any additional comments?

The video listed below shows (using the reproducer) that the first and second charts are working properly.

https://github.com/user-attachments/assets/68bbb0e1-1ee6-45e4-ba97-e74941cd49f4

The video listed below shows (using the reproducer) that the third and forth charts are **NOT** working properly

https://github.com/user-attachments/assets/0da02aa4-b15c-4269-acad-6da61fbae351

Note: The reproducer was based on Echarts custom series demo: https://echarts.apache.org/examples/en/editor.html?c=custom-profile