Plugins can leave behind malicious scripts in your game even after being uninstalled. This may be true for some free models too, but it’s much less likely.
If you want to check for all the scripts in your game, you can run this in the command bar and check the output:
local check = workspace
for _,v in pairs(check:GetDescendants()) do
if v:IsA("LuaSourceContainer") then
local thing = v
local chain = thing.Name
while thing ~= check do
thing = thing.Parent
chain = thing.Name .. "->" .. chain
You can change the ‘check’ variable to other things such as game.ServerScriptService to check inside of them instead of workspace.
As for the error, it’s possible that error in particular may have to do with ROBLOX’s recent 3-day outage. They are likely still recovering so occasional errors might be a side effect of it, but that isn’t guaranteed.