Disabling TypeScript and JavaScript Language Features built-in extension for a specific workspace helped to me (in my case the extension had been slowing down the performance of the machine and messing with autocomplete in React apps).
In your VSCode window:
Show All Commands (
Ctrl/Cmd+Shift+P) -> Type “Extensions: Show Built-in Extensions” -> Features -> TypeScript and JavaScript Language Features -> Disable (Workspace)
And reload your VSCode after that.