I have absolutely no idea what this error means or how to fix it

Message Severity: 3
.\Source\Entity.cpp(218)
Entity base class "" not found

I have, it is saying that the class specified in on of the odfs is missing, you know like

ClassLabel = "prop"

Or is incorrect but then I think it would say can't find enitiy base class such and such

What have you added recently? Or if you edited or created and odf did you perhaps delete or forget to put in a ClassLabel? There is also the possibility that one of the shipped assets you placed also has the error, not that anything Pandemic made ever has errors