Is the laptop directly connected to your router or does the connection include wall jacks, power line adapters, switches, or network hubs?
If it is only your laptop being directly connected to the router then first try another known working Ethernet cable(s).
Then try another LAN port on the router.
Verify that your laptop's network adapter drivers are up to date.
Failing that, try to bypass any interim devices and connections. Then add each one back one at a time. Monitor packet loss between each addition.
Hopefully the problem device will reveal itself when the packet loss jumps again.