Strange Google Favicon queries to API - web-services

Question

I have recently created an API for internal use in my company. Only my colleagues and I have the URL.
From a few days ago, I detected that random requests where occuring to a given method of the API (less than once per day), so I logged accesses to that method and this is what I am getting:
2017-06-18 17:10:00,359 INFO (default task-427) 85.52.215.80 - Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.75 Safari/537.36 Google Favicon
2017-06-20 07:25:42,273 INFO (default task-614) 85.52.215.80 - Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.75 Safari/537.36 Google Favicon
The request to the API is performed with the full set of parameters (I mean, it's not just to the root of the webservice)
Any idea of what could be going on?
I have several thesis:
A team member that has a browser tab with the method request URL open, that reloads every time he opens the browser. --> This is my favourite, but everybody claims not their fault
A team member having the service URL (with all parameters) in their browser History, with the browser randomly querying it to retrieve the favicon
A team member having the service service URL (with all parameters) in their browser Favourites/Bookmarks, with the browser randomly querying it to retrieve the favicon
Since the UserAgent (Google Favicon) seems to suggest one of the two latter options, the IP (located near our own city, with Orange Spain ISP) seem to suggest the first option: After a quick search on the Internet, I've found that everybody that is having such requests seem to have a California's Google IP.
I know I could just block that User Agent or IP, but I'd really would like to get to the bottom of this issue.
Thanks!
Edit:
Now I am getting User Agents as:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko; Google Web Preview) Chrome/41.0.2272.118 Safari/537.36
as well :/

Answer 1

Both of these User Agents are associated with Google's Fetch and Render tool in Google Search Console. These user agents make request upon asking Google to Fetch and Render a given page for SEO validation. This really does not make sense considering you are asking about an API and not a page. But perhaps it is because a page that was submitted to the Fetch and Render service called the API?