Character '@' always has category 'letter'

[matze-dd]

This is due to the implementation of modules for certain LaTeX packages, for instance, cleveref and glossaries. It may lead to wrong filtering as in

\textbf@

which is incorrectly parsed as unknown macro name and therefore simply ignored, consuming subsequent space.

In order to find such problems in your LaTeX code, you can use options --unkn and --list-unknown for yalafi and yalafi.shell, respectively; grep for '@'.