I get the error "Couldn't load 23 page resources" when doing the mobile friendly test at
https://search.google.com/test/mobile-friendly
However, the error message is (the rather unfriendly) "Other error."
When I visit the site in Chrome using Developer Tools and setting the device toolbar to "Responsive," it works fine with no errors, and when I go the Google Search Console and do Crawl->Fetch As Google, I get no errors.