That is because it is also send to players that didn't load the resource.
Instead, send it right back to the sender: client
addEvent("onClientSideStarted", true)
addEventHandler("onClientSideStarted", resourceRoot, function()
triggerClientEvent(client, "trig1", root, var1)
end)
See also this tutorial/enchantment, it does error handling for you as well as providing things like callbacks: