Pinging a router is totally different to the router routing packets to your destination IP address, there's no guarantee a router or node will even respond to a ping. So in other words packet loss to the 31.x.x.x addresses is just their failure to respond to pings, it might mean something, it might be a clue that these routers are flat out for example, or it might mean responding to a ping is a really low priority and they decide to ignore pings most of the time by design.
Ping plotter will almost certainly be using a tracert type behaviour to find the IP addresses of the routers / nodes, so this can be confusing because ping plotter can find an IP address that's part of your route but won't necessarily be able to ping it or not reliably ping it.
I'd focus on the destination IP address - what pings you're seeing there and if there's any packet loss, that's the result that really matters, that will be in effect what your online game will be receiving / having to deal with.
Overall anyone looking at this problem need to check and observe a low / stable ping with no streaming and a useless ping / ping spikes when streaming. If there's ping spikes on a quiet network then you've got a different problem or this problem on top of a problem with your router or connection to the road side cabinet.
As per what's already been stated a new router won't solve this - if you've got this specific problem, at best it'll just reduce the severity of the problem from 'pointless even trying to game' to a 'rage quit level' of annoyance.
