About the internet , talk to your ISP, see if they can check things are okay. Do a speedtest once in a while. Reset the modem, make sure if you did any changes to settings in it to do them again, or just try as is first. Maybe it needs a firmware update as well, can check for that too.
For more performance would i not take a whole new paltform, would just upgrade the cpu to one of the new 5000 series. Best case for gaming the 5800X3D, still very good 8 core the 5700X, or for a 6 core the 5600. Can compare prices with the previous already out cpu of the 5000 series and even check for good used options.
Weird one is that you seem to get more troubles as time goes on in game, does the ram go full? Maybe a memory leak somewhere ....
About a true new windows install, might be good, can only leave that choice up to you.
Can do a log, maybe we can see if that shows something that is out of the ordinary,
How to make a log,
you can upload it onto a site which facilitates this like
SaberCatHost this one i like since not so much (or any) spam comes with it and does not require a log in to get the info.
Just make one until this happens like you described.
Don't think i asked before. Is a bit too elaborate these days for my liking. He imo added way too many voltages. Can, in the settings, make changes to what is logged, uncheck certain items, but do it as you want and "Libre office Calc" is free so you could look as well for yourself.
Did you look at vids like this one?
View: https://www.youtube.com/watch?v=N8ZUqT6Tfiw