Header name with no header value

Without some forensic data, it is hard to say based on that single example. The User-Agent string looks legit, but is easily spoofed. I am not an expert on Google's bots, but sending an empty header like that is certainly atypical from what we would consider normal browsing behavior. You could try implementing a bot defense profile, and then allow bots at your discretion. Bot defense will challenge all bots for which you don't specify an exception and prevent them from scraping your application.