some players who does not have a blocky avatar some times experiences their head going under their waist or into their body, or just generally their characters looking very weird. I have a script that sets all the player's avatar to blocky/default R15 body, and I thought that could be the problem.

Examples:

Example 1, Example 2

my script:

game:GetService('Players').PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(character)
		local Humanoid = character:WaitForChild("Humanoid")
		workspace:WaitForChild(player.Name)
		local CurrentDescription = Humanoid:GetAppliedDescription()
		CurrentDescription.Head = 0
		CurrentDescription.Torso = 0
		CurrentDescription.LeftArm = 0
		CurrentDescription.RightArm  = 0
		CurrentDescription.LeftLeg = 0
		CurrentDescription.RightLeg = 0
		Humanoid:ApplyDescription(CurrentDescription)
		
		for _,Item in pairs (character:GetChildren()) do
			if Item.Name == "LeftUpperArm" then
				if Item:FindFirstChild("LeftElbowRigAttachment") then
					Item.LeftElbowRigAttachment:Destroy()
				end
			end
			if Item.Name == "RightUpperArm" then
				if Item:FindFirstChild("RightElbowRigAttachment") then
					Item.RightElbowRigAttachment:Destroy()
				end
			end
			if Item.Name == "RightLowerArm" then
				if Item:FindFirstChild("RightWristRigAttachment") then
					Item.RightWristRigAttachment:Destroy()
				end
			end
			if Item.Name == "LeftLowerArm" then
				if Item:FindFirstChild("LeftWristRigAttachment") then
					Item.LeftWristRigAttachment:Destroy()
				end
			end
			if Item.Name == "LeftLowerLeg" then
				if Item:FindFirstChild("LeftAnkleRigAttachment") then
					Item.LeftAnkleRigAttachment:Destroy()
				end
			end
			if Item.Name == "RightLowerLeg" then
				if Item:FindFirstChild("RightAnkleRigAttachment") then
					Item.RightAnkleRigAttachment:Destroy()
				end
			end
			if Item.Name == "LeftUpperLeg" then
				if Item:FindFirstChild("LeftKneeRigAttachment") then
					Item.LeftKneeRigAttachment:Destroy()
				end
			end
			if Item.Name == "RightUpperLeg" then
				if Item:FindFirstChild("RightKneeRigAttachment") then
					Item.RightKneeRigAttachment:Destroy()
				end
			end
			if Item.Name == "Head" then
				if Item:FindFirstChild("NeckRigAttachment") then
					Item.NeckRigAttachment:Destroy()
				end
			end
		end
		
		for i,v in pairs (character:GetDescendants()) do
			if v:IsA("Attachment") then
				if v.Name == "FaceFrontAttachment" and v.Parent.Name == "Handle" then
					v.Parent.Parent:Destroy()
				end
				if v.Name == "BodyBackAttachment" and v.Parent.Name == "Handle" then
					v.Parent.Parent:Destroy()
				end
				if v.Name == "WaistCenterAttachment" and v.Parent.Name == "Handle" then
					v.Parent.Parent:Destroy()
				end
				if v.Name == "WaistFrontAttachment" and v.Parent.Name == "Handle" then
					v.Parent.Parent:Destroy()
				end
				if v.Name == "WaistBacktAttachment" and v.Parent.Name == "Handle" then
					v.Parent.Parent:Destroy()
				end
			end
		end
	end)
end)