The google mobile friendly test conveniently shows resources that could not be loaded...but it says nothing regarding how to go about fixing them.
I know this may be a broad question, but I'm just looking for some direction on where to go to figure this out. My issue is I don't know why it isn't loading, and I don't know if the resources in question are even relevant. Attached is an image with an example.
When the Google mobile friendly test says that a resource could not be loaded, it usually means that it is blocked by robots.txt. Check your robots.txt file and ensure that you don't disallow Googlebot from crawling these resources.
You can further diagnose the issue using the "Fetch as Google" feature in Google Search Console. Plug one of the resource URLs into this tool and Google would give more detailed information about why it would not be able to fetch it.
If the Status says "Other error", there seems to be no clear reason for it but appears to happen for heavy sites loading a lot of resources. I had the same issue and after a lot of searching, this answer helped me.
To summarise it, it could just happen if a lot of resources are being loaded. As the link above states, it could actually mimic a real user on a slow mobile connection.
