Region3 Player detector is inconsistant?

I have a script that is supposed to detect players that walk into a certain area. The script displays the number of players on a GUI. The script seems to work perfectly when one player walks into the zone. However, when more players walk into it, the number of players fluctuate, especially when the players move around in the zone. For example, if there are 2 players in the zone, the number will fluctuate from 2 to 1. I'm guessing this has to do with the script having difficulties detecting the other players. How do I fix this?

local region = Region3.new(Vector3.new(-35.75, 45.35, 74.25), Vector3.new(0.75, 63.85, 111.75))
local players = game:GetService("Players")


function getPlayersInRegion()
    local t = {}
    local parts = workspace:FindPartsInRegion3(region)
    for _, v in pairs(parts) do
        local plr = players:GetPlayerFromCharacter(v.Parent)
        if plr and not table.find(t, plr) then 
            table.insert(t, plr)
        end
    end

    return t
end

while true do
	wait()
	script.Parent.players.SurfaceGui.Frame.TextLabel.Text = #getPlayersInRegion() 
	script.Parent.playersval.Value = #getPlayersInRegion() 
end