A chart is formed from various price points plotted on a graph. When a chart is open, these price points are derived from the live server, i.e from the market watch ticks. Whatever ticks are coming on the marketwatch those prices are considered for formation of the chart.
But when you open a chart midway the chart gets plotted from the data points that is already stored on the data server. Since there’s a difference between the broadcast of the live ticks and the number of stored ticks per second, there may be a slight difference in the way the chart appears.
For eg: The number of price points used to plot the graph while viewing it live maybe 4-5 but when you open a new chart, it may form from price points from the data server which may have recorded only 1 tick.