Problem:
If you use numbers as legends for spider diagram, the plots will have errors.

The following example uses "SiO2" values as legend.



The result looks like:

Solution:
Avoid using numbers as legends for spider diagram.
Pay special attention to samples names which look like "23", "3/4", "3-4" etc.
Excel might treat "3/4" or "3-4" as "4-Mar", and count it as a number.