Right off the bat... I believe you. I have spent the last year working on problems of my own and just now after a year of fiddling do I feel like I have completely figured things out... lol.
The differing mouse feel all the time and being able to manipulate it and change the feel by doing random things like you explained is exactly what I was experiencing. For me it was a lot of swapping USB devices to different ports, using USB hubs, only using a single monitor instead of 2, moving mouse cables away from LED lighting (I have some Philips Hue stuff at my desk) etc etc the list goes on. I can tell you now, some of that stuff was helpful, some of it was not. To me right away it sounds you have or had a power issue like I did. For me it became plain as day that MY particular issue was power related because I was able to manipulate my aim feel by turning my ceiling fan on and off (weird right?). My ceiling fan has 3 speeds and the mouse feel would change on each of the 3 settings, lol. I was never able to build muscle memory in games because my damn aim feel was changing every day so it was ridiculous. You said you tried a bunch of different power conditioners but those don't really do much... you are basically spraying Febreeze on a pile of poo. The only thing that would completely solve a power issue is something like a double-conversion UPS power supply because it completely isolates your devices from your dirty/messed up house power.
HOWEVER, you just said that you moved houses and still experience the same issues? That kind of puts some doubts in that theory then because the likelihood of having messed up power in your second place? Ehhh I don't know. I would only recommend the double-conversion UPS route to someone who isn't planning on moving houses anytime soon
And even then... if power wasn't your issue then a double-conversion UPS won't do crap for you and you are out some money... so it's risky. For me, I didn't care because when I realized my ceiling fan was able to manipulate my aim feel I knew it had to be an electricity issue.
Now you also started talking about stuff like your internet browser videos twitching here and there and all sorts of other stuff. It's not necessarily one thing like electricity that is causing your problems. Browser issues like that could be as simple as turning off "hardware acceleration" in Google Chrome because sometimes Chrome is dog poo. It sounds to me like you have a variety of different causes for your problems and you can't blame them all on one thing like electricity. USB devices can be another thing that cause issues I found. Plugging all your devices into a big USB hub... some USB devices might not get along with the other devices in the chain causing things like ground loops like you mentioned. Figuring it all out takes hours and hours of experimenting (like I said I was at it for like a year
). Are these devices powered via AC adapter, are they bus-powered? You have to think about all that stuff and think of possibilities where you might me introducing ground loops into your system. Lot's of different possibilities that I can't think of off the top of my head but they will come to me and I will update later.