[PC Gamer]

GeoV... from original post:

Cvars:

bot_manager_version - plugin version
bot_manager_auto_update - enables automatic updating (has no effect if Updater is not installed)
sm_bot_quota - number of players to keep in the server, use this instead of tf_bot_quota
sm_bot_join_after_player - if nonzero, bots will wait until a player joins before entering the game, use this instead of tf_bot_join_after_player
sm_bot_game_logic - 0 = use plugin logic when assigning bots, 1 = use game logic
sm_bot_supported_map - if nonzero, bots will only be present on maps that have nav files
sm_bot_on_team_only - if nonzero, players will only be considered "in-game" if they're on a team for purposes of assigning bots

So... try this in your server.cfg file:
sm_bot_quota 20
sm_bot_on_team_only 1
sm_bot_join_after_player 0
sm_bot_supported_map 1