Problem with .shell on complex geometry

Hey! I face a problem were I get
```
in ()
9 for obj in result.objects:
10 workplane = cq.Workplane("XY").add(obj)
---> 11 extruded_objects = extruded_objects.union(workplane.wires().toPending().extrude(80).faces("+Z").shell(2))
12
13

1 frames
/usr/local/lib/python3.10/dist-packages/cadquery/occ_impl/shapes.py in shell(self, faceList, thickness, tolerance, kind)
2736
2737 if faceList:
-> 2738 rv = self.__class__(shell_builder.Shape())
2739
2740 else: # if no faces provided a watertight solid will be constructed

StdFail_NotDone: BRep_API: command not done
```
When I run
```
import cadquery as cq

result = cq.importers.importDXF("/content/GitHub-logo.dxf").wires().toPending()

extruded_objects = cq.Workplane("XY") # Initialize an empty Workplane

for obj in result.objects:
workplane = cq.Workplane("XY").add(obj)
extruded_objects = extruded_objects.union(workplane.wires().toPending().extrude(80).faces("+Z").shell(2))

cq.exporters.export(extruded_objects, "/content/test/test.step")
```
It has to do with the .shell() operation, it works fine with -0.1 but I need it to be 2mm and even more If needed. What is the problem with my code? I use a dxf image of the github logo and extrude it to 80mm but I want to make it hollow with .shell(). Thanks!