Swapping out body parts and reconnecting motors creates strange physics behaviours

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#1

In my game “Colt 2” I allow players to customize a wide variety of characters. One of the customization options is having the option between a blocky and slim body. For some reason, on what seems like almost random occasions, the slim bodies make the HumanoidRootPart dysfunction and they don’t float or allow the player to move, as they’re intended to do. Sometimes even sending players straight to Position 0, 0, 0 and I don’t know why This has been plaguing me for months and I’m not even sure why this occurs.

Some things to mind:

  • Player.Character property r is changed to a pre-made rig that that is edited. This rig has the body/slim changes on it
  • Multiple players at a time seems to make this bug occur more often.
  • Only one player ever gets this behaviour inside a match
  • Occurs on NPCs too
  • Occurs more frequently on Playstation 4 in singleplayer
  • On extremely rare occasions, the waist joint disconnects
--functions that apply slim body
local libms_to_hit={
	"Neck";
	"Waist";
	"RightShoulder";
	"LeftShoulder";
	"RightHip";
	"LeftHip";
};

function setLimbStatus(char, deb)
local is_temp=false
	for i,v in pairs(char:GetChildren()) do
		local findClass=v:FindFirstChildOfClass("Motor6D")
		if findClass then
			local works=false
			for j,w in pairs(libms_to_hit) do
				if string.find(findClass.Name, w) or string.find(findClass.Name, w.."_TempBlendFix") then
					works=true
					break
				end
			end
			if works then
				findClass.Enabled=deb
				findClass.Parent.Anchored=not deb
				if string.find(findClass.Name, "_TempBlendFix") then
					is_temp=true
				end
			end
		end
	end
	game["Run Service"].Heartbeat:Wait()
	return is_temp
end

function reconnect_motors(char)
	game["Run Service"].Heartbeat:Wait()
pcall(function()
	
		char.LowerTorso:FindFirstChildWhichIsA("Motor6D").Part0=char.HumanoidRootPart
	char.LowerTorso:FindFirstChildWhichIsA("Motor6D").Part1=char.LowerTorso

	char.UpperTorso:FindFirstChildWhichIsA("Motor6D").Part0=char.LowerTorso
	char.UpperTorso:FindFirstChildWhichIsA("Motor6D").Part1=char.UpperTorso

	char.RightUpperArm:FindFirstChildWhichIsA("Motor6D").Part0=char.UpperTorso
	char.Head:FindFirstChildWhichIsA("Motor6D").Part0=char.UpperTorso
	char.LeftUpperArm:FindFirstChildWhichIsA("Motor6D").Part0=char.UpperTorso
	char.LeftUpperLeg:FindFirstChildWhichIsA("Motor6D").Part0=char.LowerTorso
	char.RightUpperLeg:FindFirstChildWhichIsA("Motor6D").Part0=char.LowerTorso
end)
game["Run Service"].Heartbeat:Wait()
end

function applyMeshChanges(target_mesh, reference, is_temp_fix)
	local newPart=reference:Clone()
	for i,v in pairs(target_mesh:GetChildren()) do
		if v.Name=="OriginalSize" or v:IsA("Motor6D") then continue end
		v.Parent=newPart
	end
	newPart.CFrame=target_mesh.CFrame
	newPart.Anchored=false
	newPart.Color=reference.Color
	local motor=newPart:FindFirstChildOfClass("Motor6D")
	is_temp_fix= target_mesh.Parent:FindFirstChild("Neck_TempBlendFix", true)
	if  is_temp_fix then
	motor.Name=motor.Name.."_TempBlendFix"
	end
	newPart.Parent=target_mesh.Parent
	target_mesh:Destroy()
	game["Run Service"].Heartbeat:Wait()
end

function applyBodyType(char, rigType)
	local SlimRig=game.ReplicatedStorage:WaitForChild("Character"):FindFirstChild(rigType)
local is_temp_fix=	setLimbStatus(char, false)
	SlimRig:PivotTo(char:GetPivot())
	applyMeshChanges(char.LowerTorso, SlimRig.LowerTorso, is_temp_fix)
	applyMeshChanges(char.UpperTorso, SlimRig.UpperTorso, is_temp_fix)
	reconnect_motors(char)
	game["Run Service"].Heartbeat:Wait()
	SlimRig:PivotTo(CFrame.new())
	setLimbStatus(char, true)
	game["Run Service"].Heartbeat:Wait()
end

--part that applies it
if CharData.BT==1 then
			applyBodyType(Char, "SlimRigRef")
		end