Cannot unwrap object

At the time LSCM was chosen as the unwrapping algorithm ABF was also evaluated but it only worked on simply connected meshes.
A logged request for implementing ABF:

@D-W I filed also a bug for the actual unwrap issue:

It’s repeatable in both 5.14 and 6.0 BETA.

The polysurface is closed but its render mesh has 24 naked edges. I tested @clement’s first macro and it reduces naked edges in render mesh to 12. It’s possible that unwrapper has problems tracking the selected seams on the mesh because of these naked edges. I will investigate this further later. Generally naked edges in a render mesh often indicate that polysurface may need some fixing - for example rebuilding edges or re-parameterizing surfaces.