WP 4.4.1, Piklist 0.9.9.6, WP Helpers 1.9.3
I realized that the excerpt box was missing from post edit pages. It wasn’t listed under Screen Options either. When I unchecked the box for “Enable WYSIWYG for excerpts” in WP Helpers/Reading, the excerpt box reappeared.
I hadn’t had this problem before, so I deactivated all plugins except for Piklist and WP Helpers, and switched to theme Twenty Fifteen. No change. Enabling WYSIWYG still makes the post excerpt box disappear.
I tested a few sites still running WP 4.3.x and they’re working fine, but I tested on another site running 4.4.1 and had the same problem there.
Donna