Consider the following two assumptions:

1. *Validity Assumption*: Assume an argument is valid. It follows all the formal logical rules of inference. The inference contains no formal logical fallacy.
2. *Soundness Assumption*: Assume the premises of the argument are sound, verified by a competent subject-matter expert.

Given the soundness assumption, the validity assumption would imply that the conclusion is logically true.

Is it possible for this argument to still be an example of an *informal* fallacy?

What makes me think this is possible is that establishing the soundness assumption, which I *assumed* to be true, cannot be done with absolute certainty. The subject-matter expert verifying the premises as true may have made an error of judgment. The validity assumption is more reliable as an assumption than the assumption of soundness since it can be checked with a computer without involving human judgment. 

This would make the list of informal logical fallacies valuable. They would be ways to test sound and valid arguments by identifying places where the argument could go wrong.

What I am looking for are examples of such situations that would answer the question in the title as "yes" or an argument that such examples are not possible. 

To repeat the question: *Can an argument be formally valid with sound premises and still be informally fallacious?*