In Microsoft Teams when any notification alert happens it doesn't display app(bot) icon.

I found that when receive any notification from MSTeams, generally we receive an application icon (bot icon) with that notification(Screenshot attached). but, recently that icon disappeared from notification. though it appears for the first time we get an bot icon but after that it  disappears.
So, is it known behavior? or something else which i am missing??  
Here i am attaching a published app notification image.

image 1.1 for the first time when i add the bot.

image 1.2  when any command executed frequently.'

Basically, it happen when i executes command in one channel frequently.