Odd internal error 500

Hello!
So I have been developing in modx for over 2 years now and this kind of problem is a first to me.

Whenever I try to access my website I get an "Error 500". But then I log in to manager and the error is gone. However, no one else can see the website.

I am using friendly urls.
The site is hosted an GoDaddy.
And also very often when I make changes the whole website is down for a minute or two. The manager, pages, everything but in cPanel it says that its up and running with no issues. I tried contacting GoDaddy but they are of no use yet.

I would really appreciate help. Thanks!

Error log:

[07-Mar-2017 14:57:39 UTC] PHP Fatal error: Call to a member function get() on null in /home/area/public_html/core/model/modx/modtemplatevar.class.php on line 296

I also downloaded the site and db and installed it on localhost to see if its something to do with the host and it turns out I'm getting the same issue when I try to access pages.