If you found that your server does not respond anything without any error message, it might be associated with the maximum number of thread in your system.
I resolved this issue by adding below lines to /etc/security/limits.conf in my CentOS 7 server.
confluence soft nofile 4096 confluence hard nofile 8192 confluence1 soft nproc 4096 confluence1 hard nproc 8192 confluence3 soft nproc 4096 confluence3 hard nproc 8192