Hey there! I edited your post to remove the domain, but I do see things working well when I checked on my end just now. If the issue is happening with a certain connection it is most likely an issue with a firewall or similar security tool on the system, such as cPHulk.
If you go to cPanel >> Errors it should give you some more detail about the problem. If you don't see helpful information there, you'd want to contact the hosting provider to have them check things on their end, so they would have full access to the server and logs to identify the issue.
