Thanks for pointing this out. The issue seems to stem from
In[27]:= Entity["Chemical", "Crepenynate"]["FormulaString"]
Out[27]= "C18H30O2"
In[26]:= Entity["Chemical", "Crepenynate"]["VertexTypes"] // Tally
Out[26]= {{"C", 18}, {"O", 2}, {"H", 29}}
In this case, the "Formula" is entered incorrectly, which led to this entity being in the "C18H30O2" entity class. I will file a bug report.
