In addition to the "loop" posted above by Romain Picot:
In case the unreproducible error stays visible on one side, but is not to detected on the other side, I strongly suggest to send this person to the Bugtracker of the used Software and/or Linuxdistribution (for example the Debian or Ubuntu bugtracker) and ask them to have a look at the discussion regarding the issue discussed at stackexchange.
In many cases unreproducible errors are "real"[¹], they just don't show under any conditions. It may happen for example that one problem occurs only in conjunction with other packages installed, or only if an underlying library has build in version x, or only if you are on a certain kind of hardware.
Having a broader overview of the used components is only possible if people know this system from heart. Sometimes these people that can help better with system debugging than the "avarage tex wizzard" ;)
Thats why software projects in general and Linux Distributions in particular have Bugtrackers - please do use them.
¹: not-that-serious-sidenote: compare Heisenbug at Wikipedia
"a heisenbug is a software bug that seems to disappear or alter
its behavior when one attempts to study it"
(Wikipedia contributors, "Heisenbug," Wikipedia, The Free Encyclopedia,
(accessed October 22, 2015).)