Wait for an update to the app. That's what you can do. Or try resizing the tile. The Outlook mail app tile on my start screen had been blank once, which was fixed after I resized it. Hard reset it an option but is not worth it for an app like Calculator.
Also, Store doesn't always show updates available. Go to Calculator's store page and wait for it to check if an update is available.
Yes I agree that hard reset is not worth it for calculator especially since it is working fine.
I have been to Store and checked on Calculator's store page.Nothing there.
Resizing tile too did not help - blank tile persists ..
I will wait for an update to the app ,though I think Calculator hardly gets any updates.
Storage says that app is ' unavailable ' (Screenshot )
BTW ,Did your Outlook mail app in storage say 'unavailable ' at that time ?