As found in MDL-79733, the string assignmentoverduehtmlcutoffsnippet starts with a white space.

This is a problem when the string is translated because the white space is not visible in the translation interface and can't be included in the translated string.

Thanks to mudrd8mz for identifying a fix for the problem: instead of having a assignmentoverduehtmlcutoffsnippet string, we need to have 2 versions of the string assignmentoverduehtml, one including the snippet and one not.