The problem might be related to a Google Chrome extension.
Extensions are synced across computers through the Google Accounts settings. Some extensions save the extension settings on the cloud, so they are synced across computers, too.
The above is because the keyboard shortcuts mentioned in your answer, Ctrl+Shift+1 and Ctrl+Shift+2, should be listed in the help articles about keyboard shortcuts for Chrome and YouTube.
To view the YouTube keyboard shortcuts, go to https://youtube.com and press Shift+?
To view the Chrome keyboard shortcuts, go to the help article Chrome keyboard shortcuts.
Next time, you can just reset Chrome instead of reinstalling Chrome when troubleshooting a problem like this. For details, see Reset Chrome settings to default. Still, before doing this, you might want to try using Chrome in incognito mode with all the extensions disabled.