Log rotation stopped working

I had a cronjob set up to rotate the Traefik logs and it's stopped working.

This is the command I had set up in crontab

docker kill --signal="USR1" $(docker ps | grep traefik | awk '{print $1}')

It used to work absolutely fine but seems to have stopped. I don't know when but I have just noticed it today.

I see the following entry in the traefik.log file
level=info msg="Closing and re-opening log files for rotation: user defined signal 1"

but it's appended to the existing file and not actually deleting the file and recreating it!

Has anything changed?