So for about a week now, I've been having these issues (that I assume are related somehow) with web browsers and certain programs. In pretty much any web browser I use, videos have a lot more trouble loading than they usually do. Instead of loading instantly (which they almost always do, I get about 90-100 Mbps download speed with a wired connection), they freeze up on the thumbnail and stay like that for at least 30 seconds or more before finally allowing me to start the video. Also, sometimes these videos will start with no audio, meaning I have to constantly refresh the page and wait roughly 30 seconds every time until I'm lucky enough to get the audio working. I usually use Google Chrome, but the issue persists regardless of the browser I use, and it'll happen on pretty much any kind of video player; Youtube, Facebook, GIFs, doesn't matter.
I also have loading issues with certain programs. Discord, for example, has a long delay before I can connect to any voice channel. The connecting process gets stuck on "Authenticating" for a good while. There also seems to be some sort of audio delay associated with Discord. Any sort of sound effect that is supposed to play, such as when recieving a message or when someone joins your voice channel, is delayed so that I hear it 5-10 seconds after I'm supposed to.
At first I thought the issue was with my computer, so I tried restarting my computer, defragging my hard drive, checking task manager to make sure there aren't any processes running that I don't recognize and to make sure there's nothing eating up my RAM or CPU usage. I've also installed any pending driver updates and Windows updates.
I also figured my internet could be the problem, so I tried restarting my router, but that didn't seem to fix anything. I then tried flushing my DNS cache and disabling adblocker, neither of which helped.
In any case, the issue only seems to be with video players, as well as programs that rely on audio such as Discord. I have experienced some loading issues with certain online games, but they seem to be random and only happen on certain games, so I won't worry about those problems for right now.
I should also mention that that recently, we installed a new modem in my household. Comcast sent us a new modem, saying that we needed to replace our old one (even though nothing seemed to be wrong with it). I personally can't tell the difference between the old and new one; it looks the same and the internet speed is just as fast. I'm not entirely sure if the issues I'm having are related to the new modem, but I guess it's possible. The strange thing is that no one else in the house is having these issues on any of their devices. It's just happening to me on my desktop.
For reference, I'm running Windows 8.1 on my desktop.
Anyway, I've never experienced any issue like this before, and Google isn't helping at the moment; the issue seems to be a bit too oddly-specific, as I haven't found anyone else with these kinds of problems. Can anyone point me to some new solutions? I'm not sure what to try next, and I don't even know if the issue is with my computer or if it's related to our internet.