After a group is modified ("updated" in Signal's jargon, see #6193) the other users just see a "Group updated." message if one user was added, or "Group name is now 'newname'.". These messages should show who made the change, for example:
"Masha added Alice the group."
"Masha refreshed the user list." <- Group update received, but with no new members
"Masha renamed to group to 'newname'."
There is an open PR which addresses improving the group update behaviour : https://github.com/WhisperSystems/Signal-Android/pull/5416
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There is an open PR which addresses improving the group update behaviour : https://github.com/WhisperSystems/Signal-Android/pull/5416