Slow download speeds?

I have a "superfast" plan, but I only 25 to 40 Mbps download speeds; my upload speeds are normal at over 150mbps. I'm not sure what the issue is. I was getting 500 to 685 Mbps until recently (and have made no equipment changes). My modem is a Netgear CM2050V-100NAR Nighthawk Multi-Gig 2.5Gbps Cable Modem for Xfinity Voice and my router is an Asus ZenWifi XT8 with two mesh nodes (also XT8s).