We recently updated an older site to Wordpress 5.3 and Divi theme 4.0.6, hosted on the Pantheon platform.
In doing so, we quickly found that we could no longer edit our pages as the Divi builder would not load. The error in the error logs was:
.../data/Utils.php:758 ET_Core_Data_Utils::WPFS():
[ERROR]: Unable to write to filesystem. Please ensure that the web server process has write access to the WordPress directory.