Apache :: Access Log Missing Entries

I have a lamp server setup with a couple of vhosts. Investigating the log files for a situation I found that it seems to be missing some entries. The access log contains a long list of files (images and css) requested by the client regarding a request to a page (having a specific url as referer), but the actual request is missing. The url called is an automatically generated url that should only be available as an unsubscribe link in emails send to a specific user, thus the use of it in the logs is limited

At the same time I can find log entries in our database that I am 99.9% sure can only originate from this specific URL being requested (never say never). These log entries are stamped just before all the auxiliary requests having the url as referer, but again the actual request is not to be found.