Hello 
I am stuck a little bit with changing the system user avatar. Until now I used the use_site_small_logo_as_system_avatar setting but now I want to change it with custom image. So I went to system user preferences and upload a new profile picture. It seems it changed everywhere to the new avatar except the notifications icon avatar (user menu and notifications page), where it use the letter avatar. But I see in Meta it seems works with the custom system avatar.
On my site it uses the letter avatar after changing to custom image.
What am I missing? Thanks 