Weird requests filling apache access logs
You're looking at a hex-escaped string.  After some googling, I found this entry on server-fault:  https://serverfault.com/a/758511/90491.

You're looking at a non-decrypted HTTPS request.

From Link:


  You are most likely seeing this because you are making an HTTPS request to an HTTP endpoint. For example, you're sending an HTTPS request to port 80 of your web server instead of 443. As a result, the HTTP endpoint gets a bunch of encrypted data, makes no effort to decrypt it (since HTTP is supposed to be plaintext), and so you get a bunch of gibberish in the log file.