discover what is hanging the process in WP (typically a module in the plugin that is out-of-date or simply calling some DB lookup that is not completing)
Whats with the UCP rather then CPU. I run a few Wordpress sites and no issue so its don’t think this is a Virtualmin issue rather a wordpress issue.
This may help
Each of those SQL invalid requests will start a new process which will hang unless handled correctly. how many of those requests (potentially queued) can you put up with waiting on a timeout? Each failed SQL is clogging up the system it could be locking tables - further adding to the problem. Bad lazy coding is the bane of PHP and WP is full of it.