Getting "Could not read config file" error during product save

Looks like a permissions issue to me, possibly with a module xml file. If you've recently upgraded, have you set permissions for the new files?

Magento reccomend the following for a multiple user site (ie, you're editing files with one user, and the hosting software such as Apache/Nginx is running as another user):

cd <your Magento install dir> find var vendor pub/static pub/media app/etc -type f -exec chmod g+w {} \; find var vendor pub/static pub/media app/etc -type d -exec chmod g+ws {} \; sudo chown -R :<web server group> . chmod u+x bin/magento 

The web server group on Ubuntu or Debian is typically www-data.

If it's a custom module you can change permissions for every file and directorry in app/code, or set the specific module path to affect only that module:

find app/code -type f -exec chmod g+w {} \; find app/code -type d -exec chmod g+ws {} \; 

Reccomended reading for more info on Magento 2 permissions: https://devdocs.magento.com/guides/v2.0/install-gde/prereq/file-system-perms.html

cd <your Magento install dir> find . -type f -exec chmod 644 {} \; // 644 permission for files find . -type d -exec chmod 755 {} \; // 755 permission for directory find ./var -type d -exec chmod 777 {} \; // 777 permission for var folder find ./pub/media -type d -exec chmod 777 {} \; find ./pub/static -type d -exec chmod 777 {} \; chmod 777 ./app/etc chmod 644 ./app/etc/*.xml