Yeah, if you use just the Delete key on edges, it leaves all the vertices behind at the intersection points. Ctrl + Delete will remove the intersecting vertices. You can try making a marquee selection through the center part of your model while in vertex selection mode to grab any stray points, then press Delete (not Ctrl…
Ah, yes. So if you refer to my clarification above in post #18, you'll see that Ctrl + Delete with vertices selected will delete all connecting edges. So in the case of vertices, you just want to use regular old delete key if you want your edges left intact.
Those points you have selected are all floating on an edge. If they were quads to begin with, those extra verts bump it up to 5 sides, even if 2 of those sides are adjacent to each other. You will need to remove extra vertices or connect them with edges in order for the polygons to work as quads.
If you have triangles or ngons, your insert edge loop tool will not know how to split a polygon. Sometimes you can get floating vertices along edges if you are just starting out which happens when you delete edges/edge loops using the Delete key (never do this; use Ctrl + Delete or the Delete Edge/Vertex tool instead).
Try selecting your object and doing a Mesh > Cleanup with the following options: Operation: Select matching polygons Scope: Apply to selected objects Keep Construction History: checked Faces with more than 4 sides: checked (all other checkboxes in this section left unchecked) Lamina faces: checked Nonmanifold geometry:…
If your Cleanup selects any faces then there is some sort of problem with them. Usually if a face is selected from the Cleanup tool it indicates ngons. They will cause problems if you don't fix them. When you have unexpected ngons or other weirdness, your modeling tools begin to stop working as expected. Insert Edge Loop…