Comment 2 for bug 1779171

In this specific case, the problem seems to be permanent, because the /etc/cron.d/rabbitmq-stats file is simply missing from the filesystem:

root@juju-21ef40-17-lxd-6:~# ll /etc/cron.d/
total 20
drwxr-xr-x 2 root root 4096 Jun 14 20:00 ./
drwxr-xr-x 105 root root 4096 Jun 28 06:22 ../
-rw-r--r-- 1 root root 589 Jul 16 2014 mdadm
-rw-r--r-- 1 root root 102 Apr 5 2016 .placeholder
-rw-r--r-- 1 root root 190 Jun 12 08:21 popularity-contest

However, the cron scheduler have a valid value:

$ juju config rabbitmq-server
  ...
  stats_cron_schedule:
    default: '*/5 * * * *'
    description: |
      Cron schedule used to generate rabbitmq stats. To disable,
      either unset this config option or set it to an empty string ('').
    source: default
    type: string
    value: '*/5 * * * *'

And the juju unit log have the following entry:
2018-06-14 20:00:35 DEBUG juju-log cluster:43: Writing file /etc/cron.d/rabbitmq-stats root:root 444