According to your htop screenshot it seems that DHIS2 (Tomcat) is not running. I might be wrong as the output is trimmed but I don’t see a process of Java / Tomcat running.
Have you followed any specific guide to install it? Maybe you have not enable Tomcat as a service? Or have you forgotten to launch it manually?
Actually, last friday, I restarted the VPS and the issue was solved (For the moment, all is working normally). However, I am very intrigated…Is a DHIS2 instance in 2.34 RAM high performance?
Not really sure what do you mean by your question. DHIS2 will perform very differently depending on the size of your database, and even then, it depends on the number of TEI or Datasets.