I noticed that it was stuck on Feb 2. It's last lines were:
[MSK Jan 28 05:39:30] info : Reinitializing monit daemon
[MSK Jan 28 06:06:15] info : Starting Monit 5.14 daemon with http interface at [127.0.0.1]:2812
[MSK Jan 28 06:06:15] info : Starting Monit HTTP server at [127.0.0.1]:2812
[MSK Jan 28 06:06:15] info : Monit HTTP server started
[MSK Jan 28 06:06:15] info : 'mariadb-02.local' Monit 5.14 started
[MSK Jan 28 06:06:16] error : 'memcached' process is not running
[MSK Jan 28 06:06:16] info : 'memcached' trying to restart
[MSK Jan 28 06:06:16] info : 'memcached' start: /etc/init.d/memcached
[MSK Jan 28 06:07:17] info : 'memcached' process is running with pid 1029
If you use monit in LXC, we recommend to upgrade to the upcoming monit 5.16 release (should be available today) - it comes with fix related to LXC (if you have some process check with a connection test, the connection test was skipped, as it was not possible to collect part of data inside LXC container).
I think it should be possible to trigger the problem without involving monit, the following script collects the data from the /proc filesystem each 5 seconds similarly to monit, can you try to run it and see if it'll stuck as well?
do cat /proc/meminfo /proc/stat /proc/[1-9]*/stat /proc/[1-9]*/status > /dev/null