Issues such as https://gerrit.wikimedia.org/r/#/c/266662/6/includes/specials/SpecialContributions.php shouldn't be possible without leaving something behind in the PHP error log. It's essentially a PHP Notice for undefined variable, except that it's through indirection of TemplateParser (and LightNCandy).
These are still immature and shows in lack of error handling.
It seems LightNCandy has some error options. Not sure which ones to use and how we'll forward it to the appropiate logs.