Question Internet only slow in-game

Apr 29, 2020
TLDR: When playing online games (Modern Warfare, Apex, etc.) my connection speeds show massive drops as soon as the game is loaded, even when using Ethernet. As soon as I quit the game, the connection shoots back to normal. HOWEVER, when at a different house with a different ISP, connection is stable. Is this an issue with my setup, modem/router, or ISP? please cure me of this cancer thanks

Intel i7 8565U 1.8GHz
Nvidia GTX 1050 MaxQ (if it matters)
So our we recently moved into this house and got WiFi via Spectrum and bought a new router etc etc. Internet was subpar but definitely usable, but Spectrum sent a technician anyway to check things out, and after fiddling for 10 minutes he comes back and says the modem was getting too much power and that he adjusted it. What could this even mean? After that I have been I experiencing the following sequence of events, not with every attempt but the majority: 1) Game unopened, WiFi stable, ds averaging ~300Mbps, us~50Mbps using 2)Launch game, connection still stable. 3) Load into match, connection drops to 1 bar, ds~120kbps, us~70kbps. Unplayable lag, 999 ping, and severe rubberbanding. 4) The instant I quit the game application (rage quit mind you) the connection shoots back to normal.
These symptoms seem to occur independent of time of day and number of users on the same network or lack thereof. I have cleared caches, updated drivers, connected via Ethernet, and installed a VPN, all to no effect whatsoever. Additionally, the issues are only present using this network i.e. when at my parents' house (whose internet package is supposedly SLOWER) I have no problems. Is this likely an issue on my end with my setup, or is Spectrum at fault? I would rather resolve this here first than spend 3 hours on the phone with my ISP again to get someone to come down and investigate. Thanks
Jun 11, 2020
I had this same problem and currently do. I temporarily solved it by changing the firewall settings of my router. If you're connected to the wifi you can access the router settings through your web browser and disable or lower the firewall.

If you have comcast type into the address bar and login. The username is admin and the password is password. from there you can change the wifi security settings.