There are a million reasons this could happen, running out of resources is just one of them, configuration of the OS, PHP, WP, MySql, Apache, etc… all could be issues.

First thing to do is track down what errors you’re finding in your web logs.

Another important thing to understand: Monitoring is like taking a picture of the state of something very specific every 5-60 minutes. Your site can be unresponsive in 10 seconds and back to responsive in another 10. Monitoring may completely miss your problem because it is not configured to debug or troubleshoot performance, but instead understand capacity usage over time.

Chances are you’re trying to use the smallest possible droplet size and you’re swapping out to disk or running out of memory at peaks and things stop responding.

Watch out for bots, Google analytics does not record bots traffic, What I do is monitor the server logs, I see bots request. even if google does not show any active user.