This issue is unrelated to Admin Tools. In fact, this issue is not really implemented in Admin Tools itself but your web server and your browser. All Admin Tools does is create two files, a .htaccess and a .htpasswd, in your site's administrator directory. The former tells the web server "this directory is password protected". The latter says "these are the usernames and passwords allowed to access this directory".
It is up to the web server and the web browser to implement the password protection. It typically goes like this.
The browser tries to access a protected resource without sending a Basic Authentication HTTP header.
The server sees that and replies with HTTP 401 Unauthorized.
The browser sees that HTTP error and displays a popup to you, the user, to enter a username and password. Then it retries the request but this time it includes a Basic Authentication header with the username and password. If you choose to save these credentials with the browser any subsequent request to a protected resource will be sent with the Basic Authentication HTTP header.
So, either your server doesn't recognize the username / password combination your browser sends (unlikely, since entering the same thing works immediately after) OR your browser "forgets" your credentials. I would first try to check if browser settings synchronization is causing the credentials to be wiped out. That would explain why it happens periodically, predictably and for all sites. It would also address the sudden occurrence; either these sync setting changed recently, or there's a bug in their implementation after a browser update or a third party browser extension is screwing up big time.
FWIW I am of course using this feature on all of my sites, live and local. I am using pretty much every major browser out there on all major Operating Systems. I have not seen that issue. But I do understand that bad sync settings would most definitely cause it. That's why my educated guess is to start looking for a sync issue; that's what I'd do if I had the same problem.
Nicholas K. Dionysopoulos
Lead Developer and Director
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