why does a black box appear when I close an app

[Android Central Question]

a small rectangular box with rounded corners appears at the bottom of my android homescreen for a few seconds whenever I close an app.

 

[belodion]

What device is that?

 

[Angloberry]

Huawei P20 Pro, I think it started happening after the last OS update 9.0.0.163 (C432E5R1P9patch01) It appears for a few seconds on all of the screens not just home but only when an app/apps are closed. If they are minimised or you hit the centre home button it does not appear

 

[belodion]

Okay. Thread moved to that forum.

Welcome as a new member.

 

[B. Diddy]

I wonder if it might have some kind of message in black lettering. What happens if you set your wallpaper to a light-colored image -- does anything show up in that box?

 

[Gillingham FC]

It's where the app is closing and the phone is saying it's in optimal condition.

Have you set app closure to aggressive? as it should only be saying that when you close all apps.