Notifications add/edit page is consuming too much memory for sites with many taxonomies

[andergmartins]

The user has thousands of taxonomies, more than 200K users (but only 50 authors), and the notifications add/edit page is not loading unless he increases the WP_MAX_MEMORY_LIMIT to 1GB.

[CodingSamurai]

We're having a similar issue. 53K taxonomies and it's nearly impossible to edit the workflows. We also have over 150,000 users and that causes memory/performance issues on the Post Edit page due to the Notifications metabox.