Hi. I have the same problem, after installing the new version my pages "vanished". I had to roll back to 3.8.8 to restore the site.

Reinstall with SPPB 3.8.8 Pro and wait for next updates.

Hi Paul, I set up the 4.0.2. The result is the same. My pages do not displayed on the back-end and cliking on any link I got the restricted access message.

Do you have any extra ACL component, Firewall or Cookie plugin installed?

Is possible to share access to admin area (/administrator), maybe a new Super User account - if yes, please - we will check - so far it's very rare case. But it's worth to discover why it happended.

Hi Paul, This is my test site 100% identical to my ha5ao.com live site. Now I reinstalled the 3,8,8. version to let you see my PB pages. Yes I have cookie plugin installed. I use the helixultimate template on my site. On other J4 core installation with the Cassiopeia template is works fine.

Thanks for access, we will play and let you know.

Uffff.... found

If in Joomla 4 those two plugins are enabled

SP Page Builder 4 doesn't work > "Access Restricted"

so I had to disable them. Now is OK.

Paul, I disabled both plugin. Still get the restrichted access with the 4.0.2. Now the 4.0.3. version is set up and still get restrichted access message. I dnt know how did you do to see my pages.

On your testing domain was OK (at least 4h was) - that's why I made screenshot as evidence. But indeed later I enabled some old settings, components etc.

In general one of extra rules something is cut off "index.php" from the URL here

and it was something else with security rules that locks it.

That's why other users do not have this same problem.

Ok, I remember...

it's one of rules from .htaccess file that was generated by SecurityCheck Pro. But which one cause that problem you have to ask SecCheck developer. Something is wrong, maybe Exception is needed.

With default Joomla 4.1.x .htaccess file, all is OK. I set it , tested. You can check too.