This may be down to the way that charts are generated.
Each chart has a total of 10 000 data points available. If the data range includes more than this then the data is resampled before being displayed in the chart.
Resampling will involve averaging the data to create fewer data points. This will mean that some peaks will not be correctly displayed.
Additionally, the 'new' data will be confused if the update rate from the source device changed during the viewed time range. This will mean that the data will appear to have arrived separately even though it may not have. To avoid this ensure that the date range selected only includes one update rate.