Login page doesn't always load


I am setting up an internal server of rocket chat on a centos 7 server.
The installation went well, but I am having an issue where at times upon reopening the rocketchat app, it will not load the login screen fully…it sits showing the following(See attached image)

Ok while writing this, and ignoring the app for awhile the page finally loaded…
any idea why this may be?
Why would it take so long for the page to load?
We are talking minutes of waiting before the login page displays properly.