Hi toby, it might be that some of the vertices you select don't encounter the edge, but maybe the yellow lines of the mesh, preventing them from being moved further. Is this your case?

Yep, this can happen when the mesh is deformed. Uncheck Deformed in Edit Mesh mode and you can more easily see why Spine isn't letting the vertices move.

Can you post or email the project file? contact@esotericsoftware.com

You can delete everything except the problematic mesh and we don't need the images. Without being able to see the problem, it's very unlikely it can be fixed.

A friendly tip:

You can use ShareX to capture screen video.
ShareX is an free (open sourced) screen capture software. ( https://getsharex.com/ )

The GIF videos in this post is also created with ShareX:
Mesh editing bug

Thanks.

When Deformed is unchecked, you are seeing the UVs (aka texture coordinates, which are the location inside an image that is mapped to a mesh vertex) as they are. When you move a vertex you aren't actually moving the vertex, you are moving the UVs. When you exit Edit Mesh mode, your mesh vertices will not have moved, but the image will be stretched over those vertices differently. When moving UVs, mesh edges must not cross because they are used for triangulation. When Deformed is unchecked, you see the actual location of the edges, so it is easy to see why you can't move a vertex.

When Deformed is checked, you are seeing the mesh vertices (just like outside of Edit Mesh), not the UVs. When you move a vertex, Spine does some complex calculations to allow you to move both the vertex positions AND the UVs at the same time. I believe this feature is unique to Spine and it was... interesting to implement. :bang: Anyway, when you are adjusting both the vertex positions and the UVs, the mesh edges still must not cross in the non-deformed / UV view.

This is fine if all the vertex positions match the UV positions, however if you have deformed your mesh outside of Edit Mesh, that won't be the case. Handling that is what makes things complicated. When the mesh is deformed, the UVs don't necessarily move at the same speed as the vertex position.

For example, I stretched the middle of the mesh outside Edit Mesh, then with Deformed checked I moved vertex you see selected as far as I could up and right:

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First, it looks odd because edges cross. Second, why did it stop me from moving the vertex further? Uncheck Deformed to see:

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When the UV hit an edge, it stopped. The vertex position moved further because the mesh was deformed. It's OK for the vertex positions to caused edges to cross, but not for UVs.

Still with me? So, your mesh is deformed outside Edit Mesh mode. You can see it in the "missing image" X, around the mouth:

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When you try to move all the vertices except the corners, the UVs try to move in various directions and in various amounts, they hit an edge and prevent the movement.

What you can do is click Reset outside Edit Mesh mode (note that Reset inside Edit Mesh mode does something else!) to remove the deform on your mesh, then you'll be able to edit the UVs and vertex positions with Deformed checked.