I think this is an unidiomatic word choice in English arising from use of a cognate by non-native writers. This is from a document written by German-speaking authors (I won't give details in case of confidentiality issues, but it can be found on the Internet).

A delicate task or operation, in English, normally means one that is exacting, difficult to perform, requiring care and skill. But that meaning doesn't fit the context. Mathematically it is no more difficult, in principle, to divide 67 instances into subsets than 670 or 6700. The point is that it is statistically less reliable. Sub-dividing 67 cases, or even as few as 5 in the second instance, produces a very thin statistical base. I think this is the clue to what they mean by "delicate": they mean "thin", "lacking in solidity", like a delicate fabric, for example.

They were probably thinking of German "delikat", in the sense of "requiring careful handling". It can be a synonym of "prekär", precarious. This is what they mean, I think, and in principle the same is true of "delicate" in English, but in this context it's not what the word suggests and it's not the word a native speaker would use to convey the idea.