When there is only one x component at facet chart, the popup info box does not highlight the hovered series's name and value. Below is the example:https://jsfiddle.net/YeongCY/nnzwug82/
When content function is implemented to the info popup box, the second parameter ( which is called as 'activeSeries' in the example: https://zoomcharts.com/developers/en/facet-chart/examples/info-popup/contents-function.html ) always return null value when the series is hovered.
Thank you for reporting this, it does indeed look like a bug! I'll investigate this issue next week and get back to you.
This issue is closely related to this bug:
We will update this ticket when the related issue is solved.