This, at first blush, it looks like a Microsoft Hosting customer is trying to access a SharePoint file. It can be a simple on-line data collection effort or possibly a malware compromised computer seeking for vulnerabilities. It can go either way. There is very little information on this pattern yet to tell. I appears there may be malware that searches for this file, however, I could not find anything solid quickly. It appears to also be a common file for SharePoint and a request of this type may not be uncommon. I do not know SharePoint enough to comment nor am I aware of a particular vulnerability. The NVD database does not reference anything. It could be very new or nothing at all.
It is not anything I would worry too much about.
If you have SharePoint, then make sure it is up to date and secure. If not, do not worry about it- let it 404. If it is a pain, then you can block it.
RewriteRule ^/?FPURL\.xml$ - [F,L]
This likely was addressed to the server using an IP address or a domain name not defined within the server configuration files. Some Apache installs have a catch-all site enabled immediately upon install. When the request does not match a defined domain name, the catch-all site handles the request. The catch-all site uses the default log file usually found in something like
/var/log/apache2/access_log though it does not have to match this exactly- it all depends on the install package. This is likely what is happening. Still, nothing to worry about.