Just a heads-up, if anyone else like me is still looking for this feature:
To me it seems like the default hotkey Ctrl + R has been taken away in some version of Obsidian (I’m running 0.12.10). It’s quite logical to disable this feature by default, as you don’t want to accidentally hit a hotkey that reloads the whole application. If you need this feature, go to Settings → Hotkeys, type reload to the search field and then you’ll find Reload app without saving and you can assign a hotkey to it.
Or another way: In the editor, press Ctrl + P (maybe Cmd + P in Mac?) to open up a list of commands, then type reload and select Reload app without saving. This reloads the app immediately, without assigning a hotkey to it.