For a few revisions now, I have seen the following as the very first 
line of log files. It is not coming from my document. Is anybody else 
seeing it?

    fonts           > beware: no fonts are loaded yet, using 'lm mono'
    in box

Here is an example document that generates it:

    \setupbodyfont[libertinus,10pt]
    \starttext
    Hello world!
    \stoptext

It seems harmless, but it does result in loading an un-needed font.

    mkiv lua stats  > loaded fonts: 4 files: lmmono10-regular.otf,
    libertinusmath-bold.otf, libertinusmath-regular.otf,
    libertinusserif-regular.otf

-- 
Rik