Two users have recently reported intermittent faults with the same equations displaying sometimes and not others.
Viewing
http://en.wikipedia.org/w/index.php?title=User:Salix_alba/sandbox&oldid=573752375
gives Failed to parse (unknown error). Yet if I edit the page and see a preview they all render fine.
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=55709