I used the algorythm here to test PDF / A compliance :
With one pdf document (which i cant give you due to confidentiality), an NullPointerException occur here :
As i dug deeper, i found that preflight loads a font context where it puts all pdf fonts. The PDType0Font is also created and put in this context.
The problem is that at the end of one step of the analysis, the clear method is called on the PDType0Font (see eclipse-1.jpg), but the font is still present in the context. On a second step, the same font is retrieved from the context, with no data in it, and the NullPointerException occurs (see eclipse-2.jpg).
I tried the validation after removing the clear method from PDType0Font and it works just fine.
I think the problem comes from this context, and a clear on a font should also trigger a deletion in this map.