All players are always marked AFK regardless of the settings. My settings:

{
  "absoluteTimeScale": {
  },
  "activity": [
    "input",
    "loot",
    "respawn",
    "chat",
    "wakeup"
  ],
  "afkMinutes": 10,
  "clanFirstOffline": false,
  "clanShare": false,
  "cooldownMinutes": 0.0,
  "damageScale": {
    "1": 0.0,
    "12": 1.0
  },
  "interimDamage": 0.0,
  "minMembers": 1,
  "playSound": false,
  "prefabs": [
    "door.hinged",
    "door.double.hinged",
    "window.bars",
    "floor.ladder.hatch",
    "floor.frame",
    "wall.frame",
    "shutter",
    "wall.external",
    "gates.external",
	"sign",
    "box",
	"vendingmachine",
    "locker"
  ],
  "serverTimeOffset": 0,
  "showMessage": true,
  "sound": "assets/prefabs/weapon mods/silencers/effects/silencer_attach.fx.prefab",
  "VERSION": "0.4.2"
}