Cannot unmap domains

We cannot unmap domains. Error is:

Unmapping was not successful, please check your permission and try again later

WordPress 4.0
Domain Mapping 4.2.0.2 (also tested with 4.2.0.6)
Multi-Domain 1.3.4.3
iThemes Security 4.4.23

We run both the front and back end under SSL using rewrite rules:
RewriteCond %{HTTP_HOST} ^www\.(.*)
RewriteRule (.*) https://%1/$1 [R=301,L]