The torch button is missing. How do I get it back?

I've always had a torch icon in the quick settings tray, for example (from another phone): However mine now looks like this: I think it happened after I tried taking a video with the stock camera app (Nexus 5X). As a workaround I can turn it on by enabling the flash when about to record a video, but this is really inconvenient. I'd like to be able to switch it on without unlocking the phone.