5xx errors mean that the server is not able to reply to the visitor's request. There are a lot of possible causes, based on the error, for example:
Issues with the website's code: invalid syntax, incorrect parameters, an incomplete function used, etc;
Issues with plugins or themes causing server overload or logical mistakes;
Issues with order's resources limit being reached.
And many more. Before proceeding with error troubleshooting, please double-check if it's not a local cache issue.
If the issue persists even from a proxy, please check the article about the error you are seeing:
If you have any additional questions about any of the errors troubleshooting, feel free to contact Customer Success Team 😊