Could you please check if requests appear in your apache logs when you try to access mautic? Esentially, connect through SSH and have a look at the following files:
If nothing appears when you try to connect, then it's not an apache issue. Don't forget to check with the following command that the apache installation serving mautic is running fine:
sudo mautic_installation_directory/ctlscript.sh status
If none of that helps, I am afraid that it only can be an issue within AWS and their proxy side.
As a last resource, you could simply change your setup. Having two full stacks installed on different ports is actually overkill for your purpose. Both applications are PHP and pretty similar. Given the case, why don't you install a LAMP stack and afterwards install two application modules on top of it that will serve suitecrm and mautic at
If you wanted to serve some of them at a different place, you only have to enable virtual hosts. Full documentation here. The modules can be downloaded here.
We’ll be looking forward to receiving your reply.