Incorrect placement of a notehead
In the attached file, there is non-standard placement of the C4 notehead in the lower staff. The notehead should be on the right side of the stem. Note that in the inspector, "Mirror head" is set to "Auto". Also, if you delete one of the two eighth notes, the C4 notehead will be on the right side of the stem.
A workaround is to select the C4 notehead and change "Mirror head" to "Right".