Stray vertices resulting in long triangles when using unwrap

Hi, I’m pretty new to Blender and have been fooling around with some meshes to get a feel for the different tools available.
Sometimes I’ve got things looking decent, then add/remove a couple of seams and re-unwrap, then get a couple of stray vertices dragging a face across my UV map. I’ve attached a picture, you can see red slivers overlapping other faces. These vertices are not attached to any other faces, nor are they pinned. Sometimes the face in question is not attached to any other face at all, it just has 1-3 vertices on one side of the map and 1-3 somewhere entirely different.
I can make them go away if I go around and manually mark the edges as seams, which it seems they already are; or if I pin and unpin the stray vertex for each face.

Could someone tell me what’s going on and how to make it stop? Either how to make it stop happening in the first place or how to select all disproportionately long geometries and make them realise the proportions they should be?

I realise the UV map I have is too crowded to be practical, I’m still just learning the ropes, this isn’t for anything necessary.

Have you had a look inside your mesh to check that there aren’t any internal stray edges (or faces) connecting vertices on opposite sides of the object?

Thanks for the quick response.
They seem to be from small fins at the base of blades on a cooling array, they look 2D. Their normals point up where I would expect to have a face with a normal pointing down, so I’m not sure if it’s a face without a backside or two co-planar faces. I still don’t understand why the faces in the UV map would have their vertices all over the map if they’re not attached on the map to any other faces.

There’s something not right with a couple of the faces I have drawn arrows pointing too. Their shading is weird. Either their normals are wrong or they have internal faces. The good old H key can do wonders. Hide some of the polygons and see if there are any faces inside. It’s often easier than trying to use wireframe view to looks for things like that.

The two you’ve marked seem fine, the problem face has the selected edge as one of it’s edges. It seems there are two quads and three triangles occupying the same plane and sharing vertices. Is there a way to select co-planar overlaps and simplify them to something reasonable? From the brief research I’ve done it seems like too much work to bother, I think I’ll just tell my draftees to mind their 2D geometry.

Try running the remove double verticies command.

Remove double vertices doesn’t remove anything.