[FishirOne]

So as the title says. I've tried restarting my phone several times to no avail.

How do you fix this and why does this happen?

[Mr Lebowski]

Uninstall it, do a soft reset, install it again, that's what I would try.

[FishirOne]

Will I loose all my pictures sent through WhatsApp and the data?

[UchilHasmit]

Not if you have a backup.. In files search for the date the last backup was made... Before doing that.. Just unpin and repin the tile once.. Worked for me on two occasions..

[saurabh-sharma]

Well you just need to do one thing:

1. Goto Settings > Backup > Apps+Settings
2. Tap Backup now

Wait for backup to complete and reboot your phone. It'll work again.