Disable wifi and test with a LAN cable.
If lag stops, it might be a wifi driver/configuration/hardware issue
If lag persists it could be a program using bandwidth, open task manager (ctrl+alt+supr) and go to networking tab, then menu view, update speed, high. Check if your network adapter is being used while you get lag spikes.
If your network is used while you get lag spikes, you'll have to track the software that is doing this, it could even be windows/windows update
Another option is to try to run the game on other computer at the same time, to check that lag spikes aren't something new to your network instead of something on the new computer.