This thing happened to my LG G4 (Android 6.0) 2 times in the last month.
I have google play store updates on manual so once every week I manually update the apps myself. Some updates are successful but for other apps the update is downloaded, tries to update but the app doesn't appear as successfully updated at the notification bar at the top of the screen (usually it says that the apps 1,2,3 and 4 were successfully updated). No error is being displayed either.
The first time this happened (Viber app didn't properly update), the phone could not start after restart and stuck at LG logo. I had to factory reset it to make it work again.
The second time, I saw that a specific app (this time it was the android webView system app) didn't update properly so from google play store I removed it and then reinstalled it and everything went fine.
Does anybody know what is going on, why does this happen and how to stop this from happening?