I've recently noticed a blank space at the top left of the first page of my app drawer. This is with the app drawer sorted alphabetically which is how I normally have it. If I choose one of the other orderings the blank space still appears, but in a different place. For example, sorting by "Most used" it appears about half way through, after an app which I know last used back in mid-June. On the other hand, sorting by "Recently installed" it appears before an app which I know I installed only the other week.
I can't run the app by tapping on it in the app drawer - nothing happens. But if I long-press on the empty space then the "Add to Home screen" panel drops down from the top of the screen and I can drag the invisible app and drop it on to the Home screen (I can even drop it on top of another app to create a folder!) I can't run the app from the Home screen either, but if I press and hold on the place where I dropped it then the trashcan pops up at the bottom of the screen and I can drop the invisible app in there to remove it from the Home screen.
If, in the app drawer, I select "Uninstall" from the menu, no little red cross appears in the space occupied by the invisible app, so I can't get rid of it that way.
I've installed & run Malwarebytes and AVG antivirus and neither of them have flagged anything which could be causing this.
Does anyone have any ideas about how I can go about establishinig the identity of this mystery app, and either making it visible or uninstalling it?