SOLUTION : Ping spikes
Problem : Playing xbox my ping goes up and down. Sometimes the lag is normal but other times so high the game is not playable.
Other symptoms : Laptop 10ft from router also seeing ping spikes. Also noticed xbox had lag issue no matter what main PC was doing (streaming netflix or just browsing web). Also noticed ping spikes stopped if main pc was turned off. Also noticed if main pc was off and I did ping test + download speed test there was NO ping spike. This shows the ping spikes arent related to what was being downloaded.
Solution in my case : Main pc is right next to router. Used network cable and plugged main pc directly into router. Now laptop sees very stable ping and xbox is playable again. Ping is not 100% fixed but is WORLDS better.
before : ping was sometimes near 30ms but OFTEN was spiking to much higher rates
after : ping is mainly near 50s but SOMETIMES spikes to 100ms