Maybe to be review ...

A project is stored under ametys:plugins/intranet node, so ACL nodes under project are automatically synchronized into Live workspace.
But it is already the job of SynchronizeACLObserver to synchronize ACL so there is concurrent modification when updated rights on a project (ex: add or remove a member)

As a fix, the paths such as /ametys:root/ametys:plugins/.+/ametys-internal:acl.* have been excluded for LiveWorkspaceListener
Is it the best way to fix it ?

Note : another solution could be to not fire EVENT_ACL_UPDATED event when editing rights on a project. But, other observers listen this event, and may be necessary (Solr observer for example)