First, do an *admin* cleanup then type kill in console.
Respawn
When you respawn, keep opening doors in the same direction (if no direct door to the direction is present, try the one that's most likely to lead you there) until a door doesn't open
Noclip upwards
Look! GMan cubes right in your doorway!
(idk if it works for everyone but it does for me)
GL@HF