Hi there,
i think Google is having a moment, these false positives of their making seems to be on the rise.
If you check the mobile test -> View Tested Page and then click on the More Info tab, you will see Page resources
> 48/71 couldn’t be loaded
Expanding that panel you will see most of them are the Other error.
Ambiguous as that is, its when Google simply didn’t have enough crawl quota to load all the necessary resources to render you page correctly. It happens when they are busy.
I just re-ran that same test and it Passed 🙂
https://www.screencast.com/t/Irx4nxqb
So you should be able to retest those sites soon, to clear the error.
You can minimise the risk of these issues through optimizations, ideally one s that reduce resources required for initial loads.