I have also been seeing the same set of warnings 353 inparticular!
I am Also having MASSIVE issues, been through the fix instructions but still no luck.
I have stripped the site back to just one meta box using a custom taxonomy which outputs nothing but the array on the front end.
All it spits out is the warning, no array, i’ve now burnt a day trying to fix it so have now rolled everything back to the working version(7.8.3)