It seems like you are experiencing a mesh deformation issue in Spine's Preview mode that doesn't appear in the Animate mode. This could be due to several reasons, such as incorrect settings or a bug. First, ensure that the "Deformed" checkbox is checked in the Edit mode, as this can affect how deformations are displayed. Additionally, check if there are any deformation keys set in the dopesheet that might be affecting the mesh. If the problem persists, it might be helpful to verify that your Spine project and runtime versions are aligned, as mismatches can sometimes cause unexpected behavior.
If these steps do not resolve the issue, consider sending your Spine project file to contact@esotericsoftware.com for further investigation.