In one corner, where there are rocks piled up to the height of 6~8 survivors and a hunting rifle nearby, a survivor can climb along the rocks to the top platform, even to the edge of map, to avoid all attacks and chases from the common and special infecteds.
And this needs no help of sv_cheat.

Some areas will trigger the system's acid attack, others won't.
I only tested this for 12 min though.

@NgSik_tw I'll add some player clip brushes to prevent players from climbing on the rocks that way. thanks!

Navigation is a huge problem. Most of the specials are stuck. We survived for 30 minutes and the specials were less than 100 (On the official map it is more than 400).

any idea where they got stuck? that way I can improve the navmesh for them