[Dragokas]

Hi,

it's easy to reproduce.

Take sm 1.8 (linux). Leave all by default. To be more independent, remove all plugins/extensions, except:
- TopMenus (extension)
- basecommands.sxm (plugin)

Case 1.

Contents of server.cfg:

... z_difficulty "Hard" sm_cvar sb_all_bot_team "0" ...

Reboot. Result: z_difficulty = "Normal"

Case 2.

Set two lines of server.cfg in reverse order:

... sm_cvar sb_all_bot_team "0" z_difficulty "Hard" ...

Reboot. Result: z_difficulty = "Hard". (bug is fixed)

Case 3.

Return as it was before (case 1) and remove plugin basecommands.smx.

Reboot. Result: z_difficulty = "Hard". (bug is fixed)

[Fyren]

$ cat left4dead2/cfg/server.cfg
say #######################################################################################
sm version
z_difficulty "Hard"
sm_cvar sb_all_bot_game "0"
$ ./srcds_run

...

Console: #######################################################################################
 SourceMod Version Information:
    SourceMod Version: 1.8.0.6046
    SourcePawn Engine: SourcePawn 1.8, jit-x86 (build 1.8.0.6046)
    SourcePawn API: v1 = 4, v2 = 11
    Compiled on: May 20 2018 17:07:52
    Built from: https://github.com/alliedmodders/sourcemod/commit/dfd27ec
    Build ID: 6046:dfd27ec
    http://www.sourcemod.net/
[SM] Changed cvar "sb_all_bot_game" to "0".
L 05/21/2018 - 20:51:54: [basecommands.smx] "Console<0><Console><Console>" changed cvar (cvar "sb_all_bot_game") (value "0")
Connection to Steam servers successful.
   VAC secure mode is activated.
z_difficulty
"z_difficulty" = "Hard" ( def. "Normal" )
 game replicated
 - Difficulty of the current game (Easy, Normal, Hard, Impossible)

Removing basecommands is also going to remove sm_cvar.