To learn how to read these results, I’d start here:
Then, follow the link in that post specific to WinMTR, as well as the one to Looking Glass. They all provide insight into how it works.
Essentially, the thing looks for a path of all the computers your signal touches between your machine and their game server. Each one of those nodes could be the source of where an error occurs.
What you’re looking for is a set of two nodes where your Worst ping goes from a low number to a very high number. In your case, your connection between your second and third nodes shows a bump from 197ms to 1434ms. Guessing from what you said about your set up, your repeater is good, your router is good, but your first hop to your ISP isn’t. If you have another device in the mix, it could be your router/gateway.
I’ll let an expert take it from here though. They may see something that I don’t or be able to help better than I.