Hi.
Columns or units has it's default max width. As you use initialDisplayAnchor: "newestData"
, then when unit reaches it's maxUnitWidth, it doesn't grow anymore and so space in past appears. You can fix this by increasing timeAxis.maxUnitWidth
if you wish.
https://zoomcharts.com/developers/en/time-chart/api-reference/settings/timeAxis.html#doc_maxUnitWidth
timeAxis: {
maxUnitWidth:500
}