Not sure what to make of this timeout message. I have seen a discussion of it and cannot tell what to do. I select an assignment that I have made and not posted yet. It happens when I render all.
I believe the root cause is that the AJAX subroutine that calls back to the server to render each library problem (or each problem in a homework set if you use "render all" in the homework editor) is unable to connect. You can use the developer tools in your browser to verify this -- you'll probably see many 404 errors and you'll see what address the subroutine is using. A common problem is that it uses http instead of https or vice versa -- this probably due to a misconfiguration in the file site.conf. Unlike browsers the AJAX calls don't try lots of alternative methods to connect -- they just fail.