I find it rare to know why this happens but continue to work these slowdowns in the usual ways.

1. We don't share the WiFi. Gamers tend to need their own WiFi. So do whatever it takes to get your own WiFi. You can try kicking all devices off save yours to dedicating the 5GHz channel to only your use as 2.4GHz is now so crowded no tech that visits will assure you it can be fixed.

2. You mention a factory reset. This usually is OK but you didn't tell enough. Microsoft has in W10 this driver update system which at times is pure evil. You'll have a good set of drivers then Microsoft replaces them. Drivers do not wear out. My method?
a. Disable Windows Driver Update.
b. Install latest BIOS, drivers as indicated by the PC's maker.