These are the hardest to track down. My kingdom for line numbers.
Depending on the size of the project, commenting out large sections and rerunning and whittling down is often the best way to find these. Similarly, doing something like a git bisect and finding when it was introduced. Those are much more manual debugging steps than I would like, and increase the friction of adopting Dialyzer, but that’s all Dialyzer gives us for that particular error, so we can’t really give more information, sadly.
You might accomplish your bisect with a regex Dialyzer ignore file for all errors that are not that specific error, then run git bisect til it shows up, to find the change that introduced the error. That would also help you find if a dependency introduced it somewhere, per the other comment.