Same here.
Deactivated ALL plugins, no permissions issues.
Activated ONLY Swift Framework, permission issue exists. (Once deactivated, problem goes away)
Here’s error, same thing.
File Permission Issues
We were unable to modify required files. Please ensure that /nas/wp/www/staging/****/wp-content/uploads/ has the proper read-write permissions, or modify your wp-config.php file to contain your FTP login credentials as outlined here..