RE: Something went wrong. An error message is logged - But where?
The data is written to the logfile immediately. Infact &action=dumpWarningLog reads the values from that file. You can see this if you rename the logfile on disk, and try to refresh the &action=dumpWarnignLog. Then you'll get an error saying it can't open the logfile.
But the big question is; how can we get the same information in the Online environment? Since &action=dumpWarningLog has been disabled we're totally in the dark when these errors happen.