High Jitter and Latency Spikes from Gateway

Over the last couple of months I have noticed my internet has very noticeable spikes in latency, even though my router is getting 100% of my gigabit plan speed. It's noticeable the most when playing any online game or video calling. I ran a Speedtest today and the download and upload speeds are normal, except Jitter is at 70ms and the latency spikes to the hundreds several times. The only thing that we changed in our setup before this issue started is the gateway, which is currently an Arris XB7. I contacted Xfinity about this roughly a month ago, and after all troubleshooting they said the issue should go away the next day. Unfortunately, after several days the issue with the jitter and spikes in latency has returned.