No log file written to SD card with 'home built' firmware

Hi. New to building firmware - using WSL2 (Ubuntu) as the build environment.

If I checkout master (no changes made) and build plane firmware, it is created no errors (so I guess my build environment is set up ok). I can load that onto my FC (OmniBusF4) and it all appears to work - except - no log files are created.

If I load a pre-built firmware (eg from ‘latest’), logging works fine. If I re-load the firmware I built, again no logging (but the board appears to be working fine).

Any ideas? Thank you!