Hi,
The image you posted would seem to indicate that there is an issue with the way we position the anomaly marker dots on the chart for cases where the aggregation interval used to plot the data is greater than the bucket span of the job (which are displayed in the label above the chart as shown in the image posted by @richcollier.
Currently in this situation we position the anomaly dot on the chart point which is closest in time to the time of anomaly. However as your example shows, when the closest point occurs after the time of anomaly, this does not correspond to the chart bucket which contains the anomaly. Instead the dot should be placed on the chart point before the time of the anomaly.
I have managed to reproduce myself, and have raised a GitHub issue for this, and will look to fix it shortly.
In the meantime, as you found, using the 'auto' zoom interval ensures the data in the chart is plotted at the same interval as the bucket span of the job, so the anomaly dots will always be positioned correctly.
Many thanks for reporting the issue!
Pete