First things first, I believe that the URL that you should be pointing to should be localhost:8065, just in case we miss out on that small detail.
If that one checks out, let us have a look at the following to start troubleshooting the loading problem. Can you refresh the page to reproduce the issue and see if there are any log entries in the following files?
mattermost.log
nginx.log
Developer tools
If there are any, can you please attach it here so we can understand the issue better?
Do you also happen to observe this behavior on the desktop client as well?