When viewing the bacteria breakdown, why are some columns empty?

The sequencing technology combined with the bioinformatics analysis pipeline we use is not always able to determine the full classification of a bacteria down to species level. In this case, it will classify as specific as possible, for example in the screenshot below, we have bacteria from the Blautia genus, with species unclassified of ~7.6%.

If you click on the distribution or timeline for this bacteria, it will show the values for the overall genus, not just the unclassified values.