UPDATE: Changing my theme seems to have fixed the problem - but I'm not sure how to fix the original theme. Any advice on that issue is still welcome!
I'm seeing symptoms identical to this question: Backbone JS error with 4.6.4 on WP messing up contribution page set up
Pages using Backbone - particularly the "Include Profile" contribution configuration page - are broken, and the JS console says:
TypeError: Backbone.Marionette is undefined
TypeError: Backbone.CollectionSubset is not a constructor
However, the issue seems to be different than other folks experiencing it. Here's what I've tried so far (including all at once):
- Disabling all WP plugins except CiviCRM.
- Disabling Summary Fields (the only CiviCRM extension in use).
- Clearing cache, deleting templates_c.
What else can I look for regarding this Backbone error? I assume it's a collision with WordPress's Backbone, but I don't know enough about Wordpress to troubleshoot that.