Re-post your screenshot with the wireframe active (either face component mode or ‘wireframe on shaded’ viewport button). Also post a separate screenshot with smooth preview active on the mesh showing the problem area (select mesh and hit ‘3’ on keyboard, ‘1’ will remove smooth preview) - smooth preview can show a lot of geometry problems.
Also, how do you expect to know whether the problem faces are non-manifold, lamina, or zero length? Right now all you know is one of those problems are occurring and you don’t know which. 3D Art is no exception to isolation being the best problem solving method.
Without the wireframe it is not easy to tell, if it’s not a mesh overlapping your selection, you may have non-manifold geometry which is caused by a significant lack of technical knowledge and invalid modelling workflow - it’s very common for students or beginners to get result. In 7 years of using Maya I have never encountered a bug that results in non-manifold geometry slipping by me.
Non-manifold is (almost always) a very bad thing because it will cause artifacts in lighting/rendering, deformations, and simulations - it’s caused by disconnected edges/vertices, internal faces, and areas without thickness.