Visual Studio code made the decision to change the next/previous tab behavior in newer versions (using the tab selector instead of moving you to the next/previous tab). In addition, the actions don't even have the word 'tab' in them, making them really annoying to track down. To restore the previous behavior you'll need to rebind the following actions:

On OSX go to Code > Preference > Keyboard Shortcuts and search for:

workbench.action.nextEditor workbench.action.previousEditor

A config might look something like:

[
    // ...
    {
        "key": "ctrl+tab",
        "command": "workbench.action.nextEditor"
    },
    {
        "key": "ctrl+shift+tab",
        "command": "workbench.action.previousEditor"
    }
]

Hope this helps!