Straight Talk AT&T Network Issue

I have trouble connecting to a certain website using the Straight Talk AT&T BYOP sim card on my Nexus 5. The website is Chatango and whenever I try to login into my account on LTE, I receive error message net::ERR_EMPTY_RESPONSE using the Google Chrome web browser app. I also downloaded the Chatango mobile app from the Google Play Store and I receive the same error message. However, I only receive this error message when I'm on LTE or 3G. If I switch to Wifi, both the Chatango app and connecting to the site on Google Chrome works without any issues. I am running Android 5.1.1 Lollipop.

To troubleshoot this problem, I took an activated sim card directly from AT&T (not from Straight Talk) and put it in my phone and I was able to connect to the site without any error messages. I even took an activated sim card from T-Mobile and I was still able to connect to the site. It's only with the Straight Talk's AT&T mobile connection on LTE or 3G where I receive this problem. So I thought it would be a carrier issue with Straight Talk. I called their customer support and they claimed that they could not help me with the issue. They claimed that it is a "Google" problem and that there is nothing they can do, despite the fact that the site works on any other carrier that I tried it on and it works on Wifi. Can someone help me with this? I am also using the latest APN settings according to what is presented on Straight Talk's website.