After a brief investigation, I found out that for some reason Brave Image Search (imgs.search.brave.com) was being blocked on our MX as "Adult and Pornography" and "Illegal". This was after discovering that searching for any image in Brave Search only results in blank images. This is just an alternative search engine to Google and as such shouldn't be blocked.
Now with an event log full of disturbing-looking false positives, I placed the above URL into the box to check for threat categories and and then clicked the x for both categories to stop blocking the site. After a while (for some reason it wasn't instant) I was finally able to see images loaded when doing a test search.
Is there a better place to report false-positives or alert others who may be experiencing similar issues?
Ideally, instead of just the x to stop our MX from blocking the site, there should be a way straight from the Content Filtering page to report false positives. Alternatively, it would also be nice to add categories to any known bad sites that have yet to be categorized by Meraki (I know you can add a URL to the Block list under URL Filtering but content-based filtering is a little more elegant).