Issue Website and Webmail Intermitent non-accessible problem

[DACOG]

I migrated from Control panel to Plesk about a year ago. The server host a few website. Strangely, a few of them works well with problem. But there is a particular website whose accessibility became very unreliable recently. Sometimes we can access, sometimes not. An this applies symptom applies to its webmail access as well.
While other websites within this host server are accessible, this morning for instance here are the errors I got trying to access the troubled website on Firefox and Chrome.




I am suspected a mis-configuration. I have:
1. change the hosting plan
2. Change DNS
3. Even, I tried with dedicated IT address, all the same, not solution

Please help I am new to Plesk. I am new to plesk but willint to learn. I need your help to find and solve the problem(s).

 

[IgorG]

I'd suggest you ask the assistance of Plesk Support Team because detailed investigation directly on your server is required.