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I'm not sure when this started happening and it's only for a single installation of mine... but when I go to the panelizer->content tab for a panelized page and try to add panes I'm given the standard modal with the list of categories down the left hand side. When I click on a category I get the ajax (?) spinner like usual... but then the modal disappears and the page is blank (white) with the spinner in the upper left hand corner. It disappears and I'm left sitting at what appears to be a blank page (https://example.com/node/5/panelizer/page_manager/content).
If I do a view source I noticed the body tag has a style="display: none". If I manually remove that (via chrome inspector) then everything appears normally.
I haven't figured out what could be causing the issue. I've tried disabling any ajax or security (https) related modules to see if that was the culprit but so far I haven't figured it out.
Any suggestions on where to look?
I've also attached the source of the blank page.