A user attempting to review the new analytics functionality reported this to me. Steps to reproduce:

login to qa.moodle.net as manager

click "Site administration" menu

click "Analytics models"

Next to "Students at risk of dropping out" click Actions and select Edit

Attempt to choose a "Time-splitting method," e.g. "Quarters accumulative"

Click "Save changes"

 
Invalid permissions detected when trying to create a directory. Turn debugging on for further details.

More information about this error
 
Debug info: /var/www/vhosts/qamaster.moodle.net/data/models/1/1507200257 can not be created, check permissions.
Error code: invaliddatarootpermissions
 
Stack trace:

• line 1551 of /lib/setuplib.php: invalid_dataroot_permissions thrown
• line 1290 of /analytics/classes/model.php: call to make_writable_directory()
• line 1457 of /analytics/classes/model.php: call to core_analytics\model->get_output_dir()
• line 440 of /analytics/classes/model.php: call to core_analytics\model->clear()
• line 129 of /admin/tool/analytics/model.php: call to core_analytics\model->update()