In pingplotter, if you test any website, does that first hop get around the same packet loss?
What firmware do you have on the router?
Maybe reset the router and setup again. Possibly reflash the firmware or if you have the latest, maybe downgrade the firmware to an earlier version and test again.
If you get the same results, from multiple devices, wifi and ethernet, router is definitely defective. You should not be getting 50% drop on the first hop. Fact is from multiple devices, router is the issue.