This issue has been successfully reproduced on the following OSes:

• Fedora 28
• Fedora 29, JDK 8
• RHEL 7.7, JDK 8

This issue is not reproducible on the following OSes:

• OS X, JDK 11
• Windows 10, JDK 8

Details describing this issue:

There is "openInIDE" used in 3 places in "main.min.js" in central source code*. When the central reloads and works normally, "openInIDE" is a function (probably defined in Java code or somewhere out of the "main.min.js" file) with following implementation:

function openInIDE() {
var result = callJava(1, '9aee3b4a3f3b40ed26f47d66375b25e3', Array.prototype.slice.call(arguments));
if (typeof result == 'string' && result.indexOf('org.eclipse.swt.browser.error') == 0)

return result;
}

After the issue appears, "typedef openInIDE" is undefined, which causes probably the issues.

*Additional information to the 3 places, where "openInIDE" appears - it appears in 2 functions:

• registerButtonClicks() - here is the "openInIDE" needed for loading and displaying the central correctly
• delegateToIDE(a, b) - here is the "openInIDE" needed for opening the wizard to the quickstart

OLDER DESCRIPTION (does not describes the issue enough, but I decided to keep it for more details about the issue):
----------------------------------------------------------------------------------------------------------------------
Sometimes central examples wizards fail to load and modal dialog is shown instead (screen attached).

Nothing in Error log view.

Restarting devstudio solves the issue.

Adding screen and central tar of:
devstudio-12.9.0.GA-v20180928-1629-B3448/workspaces/workspace/.metadata/.plugins/org.jboss.tools.central/central

Addition info:
Considering that central itests fails for this sometimes fresh installation without restart may cause this. Although it happen again after running devstudio for some time and restarting Central view.