Look for those two ip addresses in the logs (you can use the Find in log files search box in the log viewer).
I bet you’ll find a “strange” request in the httpd access.log.
Nothing to worry about. However, fail2ban could probably block more attempts from the same ip (not your case, you received only one probe).
@Adam_S, is this a production server? If it is so, I recommend taking a look deeper at the logs…and perhaps also to what @jackyes recommends. It might be more or get more serious. Take a look at it, apply as deemed necessary then upgrade once it has been made stable.
In a production server I recommend you to use at least the Firehol level 1 and 2 blocklist.
In that way you have a basic protection from the most active attacker, botnet, ransomware, malaware, etc…