*) If you add mail users under same domain as alias members, iRedAdmin-Pro will verify whether they (mail users) exist or not. If not, iRedAdmin-Pro will silently discard it.
*) The typo/render in your screenshot looks weird, it should display one member in one line, not multiple members (email addresses) in one line.
another problem is every time i add new member is existing aliases the old member is gone, also in the database, it's also gone. and the restriction also not work,i already set it to "Users under domain", but still can recieve email from yahoo, gmail, etc
Not sure why it happened on your server, sorry.
*) Did you upgrade iRedMail to the latest stable release?
*) Alias restrictions requires iRedAPD, do you have the latest iRedAPD (v1.4.0) running?