Gig speed internet slowing down drastically for several days

For the past few days, my Xfinity gateway has been intermittently slowing internet speeds to as little as 10 percent of our Gigabit plan. This is happening on all of our devices. After I tried restarting the gateway, the internet completely dropped despite the white connected light showing. When the connection comes back it is still much slower than the speeds we normally get and we experience latency spikes.

My gateway is the Xfinity XB8 and I've noticed in the router admin page DRAM is almost completely full (960MB used out of 1024MB), not sure if this is affecting it. In the Xfinity app network test, it says everything looks good and that the gateway is getting the full plan speed even though it's not.