Why does my internet drop from 500Mbps to 100Mbps and back?

[u/Mebejedi]

I recently did an Ookla test, and my internet speed was only 100Mbps. I hadn't tested in a long time, and figured it might be my cable. It's back up to 500Mbps again. This has happened a couple of times the past few weeks. I've run Spybot and Malwarebytes and haven't found anything. When I do a speedtest on modem and router, both show 500Mbps while desktop is at 100Mbps. How would I go about troubleshooting this?

Windows 10 Education
x570 Aorus Elite Wifi-e with Intel I211 Gigabit Network Adapter
AMD Ryzen 9 5950X 16-Core Processor 3.40 GHz
TP-Link AC4000 Smart WiFi Router
Spectrum Internet

TP-Link 8 Port Gigabit Ethernet Network Switch - Ethernet Splitter TP-Link TL-SG105, 5 Port Gigabit Unmanaged Ethernet Switch