Form Manager page does not work after republishing several times.

Prereq.: Open Studio editor on one page and Content / Form Manager on another.

Steps:
1. Create a new Landing Page.
2. Add Form block (with mandatory settings).
3. Add a simple form field e.g. Single Line Text.
4. Submit.
5. Publish.
(adding submissions is optional)
6. Edit.
(modifying settings is optional)
7. Publish.
8. Load Form Manager page.
9. Repeat steps 6-8 until you have 6 versions of the Landing Page (screenshot 1).
Actual: Form Manager page stops loading, error occurs "Failed to load 'http://ez6.lh/pjax/form/list'" (screenshot 2).
Expected: It's possible to load the page w/o errors.

Remarks: If the affected LP is on the second page of the Form Manager table then error occurs when trying to change to second page (screenshot 3).