The logrotate script provided by MaxScale performs log rotation by sending the SIGUSR1 signal to the maxscale process as a postrotate action with

kill -USR1 `cat /var/run/maxscale/maxscale.pid`

When maxscale is not running for whatever reason, and so no PID file is present, this leads to annoying cron messages like

cat: /var/run/maxscale/maxscale.pid: No such file or directory

kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]

error: error running shared postrotate script for '/var/log/maxscale/maxscale.log '

So the existence of the PID file should be checked for before using it, e.g.

test -r /var/run/maxscale/maxscale.pid && kill -USR1 $(cat /var/run/maxscale/maxscale.pid)

or

kill -USR1 $(cat /var/run/maxscale/maxscale.pid)  >/dev/null 2> /dev/null || true

PS: also note that the shell backtick syntax for command execution is deprecated, $(...) should be used instead these days ...