The first time I select a syntax highlighter for a “blah.blah.blah.new” file, Atom does not actually apply the selected syntax highlighting. Instead, Atom applies Plain Text highlighting.
As a workaround, I have to re-select the syntax again. This happens with C and CMake Lists syntax for example, as well as others. I suspect this is an issue with Atom itself, rather than the particular language plugins involved.
Atom 1.34.0 on Mojave.