[BC] Youtube issues

Youtube works fine if I never, ever login to a Google account. If I login to one of my accounts (e.g., to watch a video some troll flagged as mature content), my youtube performance goes to crap for several days/weeks. Logging out does nothing. I have any number of the following issues: - Videos do not start immediately. Have to F5 several times to get the video to begin playing. - Switching to 720/1080p will cause playback to freeze. Sometimes refreshing works, sometimes it doesn't. If I let the video sit, it will eventually begin playing in 360p, with the HD options grayed out. - Videos download "just in time," rather than going full speed until fully downloaded or buffering several minutes of playback. I want to emphasize that, most of the time, these issues are not present, and Youtube works flawlessly. When Youtube used to display average speed, I would see 70-80 mbps, and HD videos would download at 95+ mbps. But for a week or two after using my Youtube account, it feels like I'm on a public Russian proxy. I strongly believe that logging in to an account is the trigger for these issues, since I've observed this pattern many times over the years. It eventually goes away, only to come back the next time I login. Why does this happen? I don't understand why logging in has any effect; any network crippling would be IP-based, right? Anyone else experience this? edit: since someone will ask it, my speedtests are fine. 107 mbps from local. everything else works fine. My PC isn't garbage and isn't loaded with viruses. Cisco modem in router mode. firefox/java/flash updated.