Those file not found errors are just hackers doing scans on the system. But those scans do not affect your application. They have no effect on your performance. And from the graph I would not say that these values are sky rocketing. The app can handle much more requests per second. I do not see that connector pool shutdown warning in your logs.
And for the threadpool read this documentation: https://docs.mendix.com/developerportal/operate/trends-v4/#Trends-appm2eeserverthreadpool
You did not post the graph so I can not comment but you check if those number colaborate with the requests from webservice calls.
And offcourse you can get in touch with Mendix expert services but that is paid consultancy.
Regards,
Ronald