For some days, every time a user of our Moodle opens a task, the use of Apache CPU goes up to 100% and causes the server to collapse (we must restart it every time it passes).
We have the latest version of Moodle (3.6.2), we use Plesk with MySQL and PHP 7.2.
I have checked that we have debugging and theme editor functions disabled, but we do not know what to do. Any ideas? We will be very grateful!
Thanks a lot!

CPU | Intel(R) Xeon(R) CPU E5620 @ 2.40GHz (1 core(s)) |
Version | Plesk Onyx v17.8.11_build1708180301.19 os_CentOS 7 |
OS | CentOS Linux 7.6.1810 (Core) |
RAM | 2,80GB |
If so, the obvious thing to investigate is a lame file system. Could be database store or the moodledata directory.
The CPU is Xeon E5620 with 1 core? (The Munin graph confirms that.) But E5620 is 4 core 8 thread CPU. How do you explain that?
About Swap: The machine should never swap. It is there for an emergency. The machine has 2 GB RAM. It is possible that this is the problem (or one of them). Study the other Munin graphs like load average and memory usage.
Hi,
For a week (Upgrade from Moodle 3.5.3 to 3.6.2) , we are encountering the same problem : some tasks (for example : editing a course or displaying results in tests) crash the server. Here is a screenshot from my Virtual Machine (Debian 9.3 + Apache 2.4) on VirualBox which is a copy of the production server (3 servers with Debian 9.6 + Nginx).
My system administrators and me have not found the origin of the problem :/