[PORTAL2 PUZZLEMAKER]  CVoxelTestChamber::Export VMF C:/Program Files (x86)/Steam/steamapps/common/Portal 2/sdk_content\maps/preview.vmf ...
[PORTAL2 PUZZLEMAKER]  CVoxelTestChamber::Export VMF success, chamber size: (8,11,9)
[PORTAL2 PUZZLEMAKER]  Compilation time (after export): 28 (ms)

VBSP failed.

Valve Software - vbsp.exe (May 19 2021)
8 threads
Using shader api: shaderapiempty.dll
materialPath: C:\Program Files (x86)\Steam\steamapps\common\Portal 2\portal2\materials
Loading C:/Program Files (x86)/Steam/steamapps/common/Portal 2/sdk_content\maps/preview.vmf
ConVarRef gpu_level doesn't point to an existing ConVar
Error! Variable "$envmap" is multiply defined in material "metal/underground_wall_metal004a_bottom"!
Could not open instance file instances/BEE2/50s/items/barrier/segment.vmf