Unwrap crashes Blender

[JanXuan]

I just started a new project from a fresh template, which I use for all my meshes.
I made a single car seat, applied seams, pressed U > Unwrap, and Blender crashed. I retried, and the same story.
Then I tried Smart UV project. No problem. Then Unwrap again and crash.
I opened the Template file and unwrapped the same unedited block, no problem.
Any idea what has gone wrong?

[kat]

If the object has no UV seams marked (Mark Seam) to split the UV map the resulting smushed unwrap can cause a crash as Blender tries to determine how it should be drawn (had that happen a few times). Try adding a seams around the back and base of the mesh to split the UV at those points, relaxing the UV should relieve that stress.

Alternatively, start a completely clean scene and Append the mesh, try unwrapping again. If you get a crash then there's definitely something causing issues between the mesh and using Unwrap.

Might also be worth checking to see if there are any manifold elements (basically a non-contiguous surface or one where surface flow is interrupted in some way, typically by vertices, edges or face inside a mesh) - in Edit Mode click Select » Select All by Trait » Non Manifold, these can cause issues with the mesh's data such that Blender can crash during certain operations. For Blender 2.8+ see how to fix non manifold issues here.

[JanXuan]

I had made seams. I had not expected a quick answer with the holidays, so I went to make it all over again, and so far no problems with the new one. I will see what happens with the old one with the manifold option.

[JanXuan]

The Manifold option indicated problems indeed. I tried to fix it but still crashed.
I stay with the new mesh and trash this one.

[kat]

Yeah depending on how the manifold issue is expressing itself Blender can be a bit stubborn in re-addressing the problem. At least you know there is/was an issue with the initial mesh.