It looks like the time series chart does not update the tooltip to show the last value.
Changing the type of the trend on the XY chart makes it a bit more obvious why that is happening:
You'll notice that the first and last points are exactly on the edges of the chart. When using the X Trace line to see tooltips, it's showing you the most recent value to the left of the current position of your mouse. As soon as you cross a new point from your dataset, that point's information will then be displayed on the X Trace tooltip.
As the last point is at the furthest to the right point possible on the chart, your X Trace information will never be displaying the value of that point.
This makes more sense in the context of live data, but it could potentially be improved for looking at static data like exists on the default chart when you drag the component in. If you want, you can submit an idea/feature request here and our developers can take a look: Ignition Features and Ideas | Inductive Automation.