Juju.worker.logger reconfiguring logging from "<root>=DEBUG" to "<root>=WARNING"

When using juju debug-log or juju debug-log --level INFO to monitor the logs as I try follow some logger.info( "wibble" ) output in my operator based charm, this happens (naturally only visible when using juju debug-log)…

unit-gm-web-9: 08:55:05 DEBUG juju.worker.logger reconfiguring logging from "<root>=DEBUG" to "<root>=WARNING"

This typically happens on deploy or add-unit, and means I now can’t trace the events with INFO.

Weirdly, this was not happening until this morning, and I’ve not updated the juju snap, or upgraded the model/controller or anything else for days, they’re all at 2.8.5.

I’ve tried bouncing the “machines” including controller machine, with lxc restart ..., to see if that clears anything out, but same problem happens after I remove the application and deploy again.

Anyone know why this is happening, and how I can tell the Juju worker that I’d like to see the DEBUG and/or INFO level messages?