On test server, how to get the error report from "An unexpected error occurred"?

When I'm UI testing on my local Indeni instance, I periodically see this:

Image title

Mostly, I don't worry about it, but sometimes, I really want to get the error report. How could I get the error report? Or, maybe there's a known place/log on the server where I can find this specific error?

This message pops up when we get an HTTP error from the server.
First clues can be found in the message iteself (when using chrome it can be easily found in chrome dev tools either as console error or in the network tab).
If you want to further examine there are varius log located in /usr/share/indeni.*/logs


Hope this helps