because if not, nothing display on wp?User need to add a profile picture in phpbb even if he have one on Ultimate Member
The user i've test had also avatar in phpBB in effect.
In theory for what the code do and i remember, the default WP avatar should display if there is not one on phpBB for the user. So if the default wp avatar is replaced by UM when it is installed, this will be displayed on last topics and as avatar in wp, as on my test i've see.
But i will test out better as i will put eyes on.