Server.cfg:
hostname			Pichu's Homebrew Server
sv_defaultgamemode		sandbox
sv_scriptenforcer		0
sv_lan				0
maxplayers			8
mp_falldamage 			1
cswep_gradualaccel_global_cl 	0
sbox_maxwire_thrusters 		50
sbox_maxnpcs 			20
sbox_godmode			0
gmod_cvars_sv.txt
"CVars"
{
	"gmod_physiterations"		"4"
	"Serialiser_SaveCompressed"		"0"
	"gmod_datastream_iterations"		"1"
	"pac_enable"		"1"
	"pac_allowbonescaling"		"1"
	"pac_maxbonescale"		"1.500000"
	"pac_maxparts"		"100"
	"pac_maxpartscale"		"2"
	"pac_maxoffsetdistance"		"100"
	"pac_maxlights"		"2"
	"pac_maxlightbrightness"		"1"
	"pac_maxlightsize"		"256"
	"pac_maxeffects"		"20"
	"pac_maxsprites"		"20"
	"pac_maxspritescale"		"2"
	"pac_maxsunbeams"		"5"
	"pac_maxsunbeampower"		"0.300000"
	"pac_maxsunbeamsize"		"1"
	"pac_maxsunbeamdistance"		"512"
	"pac_maxtrails"		"20"
	"pac_maxtrailscale"		"2"
	"pac_maxtrailfadetime"		"5"
	"pac_submission_interval"		"5"
	"sbox_maxwaterizer"		"10"
	"sv_AdvDupeEnablePublicFolder"		"1"
	"AdvDupe_NoItems"		"1"
	"TheFalcoThirdPersonValue"		"0"
	"sv_HoverDriveUseEnergy"		"0"
	"durgz_witty_sayings"		"1"
	"durgz_roleplay"		"0"
	"pac_server_outfits"		"1"
	"cswep_snapsallowed"		"1"
	"cswep_gradualaccel"		"1"
	"cswep_gradualaccel_global"		"0"
	"cswep_def_walkspeed"		"140"
	"cswep_def_runspeed"		"310"
	"cswep_roll_dmgdec"		"0.5"
	"fretta_voting"		"1"
	"fretta_votesneeded"		"0.7"
	"fretta_votetime"		"20"
	"fretta_votegraceperiod"		"30"
	"ttt_limit_spectator_chat"		"1"
	"ttt_limit_spectator_voice"		"1"
	"ttt_bots_are_spectators"		"0"
	"ttt_announce_deaths"		"1"
	"ttt_sherlock_mode"		"1"
	"ttt_minimum_players"		"2"
	"ttt_crowbar_unlocks"		"1"
	"ttt_fire_fallback"		"0"
}
I change the defaultgamemode for testing though and it won't work.
Also I've tested it with other players/bots for the same result