Some minutes ago I clicked at my Oracle APEX application menu to retrieve its list of pages, as it should be, such as in the sample below - this is what I was expecting to have in my Chrome browser.

However, after clicking, I got this instead, and I have no idea why it happened.

It vanishes after I press F5 to refresh my page, but it is currently affecting our application as well, so it's worrisome. Oracle APEX I'm working with in this scenario is 18.2 version, and Oracle database is "Oracle Database 12c Standard Edition Release 12.1.0.2.0 - 64bit Production" as well as PL/SQL release, core, TNS for Linux, and NLSRTL. Actually, "select * from v$version" retrieves these results.
Regards, Franklin