This is a question about the API, not really a bug report.
The documentation on findEssentialMat() states
Note that this function assumes that points1 and points2 are feature points from cameras with the same camera matrix.
But this is a very strong restriction. Is there a way to solve this problem between two distinct cameras?
Or would it be possible to undistortPoints() the points to normalized image coordinates with identity camera matrices for both cameras?