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

[rosenthalj]

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

- 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.

goodSmallDataCount.mov

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

badLargeDataCount.mov

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

[adaelixir]

might be related to ZRender #14920