www programming

nothing, i see that all work fine, because an avatar group, is just set up for the user like another:
avatar.driver.local
correctly processed by the code.

But there is a but and this maybe the problem instead:
if an user has been not still added into WP, because it is a phpBB user that have still not login in WP or have not visited WP side as logged in phpBB, than this user still not result as added in WP.
The avatar code in this case not retrieve the avatar for the user (until isn't added in WP side), so default gravatar display on wp side.
This can of course be changed to retrieve the avatar even if the user has not still been added into WP side.
I think this the problem.
Isn't it?
Sorry i've not think before to this possibility!

The avatar location on WordPress does work for the user's own Group Avatar WHEN the user is logged in. But only for the user's own avatar.

Other users' Group Avatar will not work though even when logged in - instead the default WordPress avatar is shown.

This is true even if the users exist in the wp_user table already

it result on db, that any avatar you choose for a group, is associated (built) into users table, for the user, as any other avatar.
So avatar.driver.local (for example) if for groups has been choose a gallery avatar.
In my test it is working fine, but i will check further more

p.s i still have not understand why the old phpBB user i have, it is a registered user, not display the group default avatar, and it belong to same group of the new user i've test registration after setting an avatar's group: the new user display avatar correctly in phpBB (so even in WP after the user has been added) while the other not (no avatar in phpBB, so no in WP).

In phpBB: the Group Avatar is assigned to the user_avatar when the user's group default is changed (through user initialization on creation or when being made a part of a default group). Existing users in a group will not automatically be assigned an avatar when you assign a group avatar to that group.

There still must be something that I am missing though as in Wordpress. On avatars in Wordpress, these group avatars do not show EXCEPT for the user that is currently logged in.

ok perfect, thank you, i'll try right now to move the old to another group so i will re-move to registered to see if it update.

But this scenario you report is strange.
In WP, the code should display default gravatar only if .... sorry, have you setup in wp_w3all admin config page the setting for avatars into widget????
Or only for WP posts?