We have exactly the same problem which started immediately after we upgraded to J3.5.1 from 3.4.8. We were already using CB 2.0.14.
I'll try the approach you suggest, Kyle, but if either of you catch the sneaky extension please advise and I'll do the same.
I do have one extra clue:
If I try to sign up a new user or edit the profile of an existing user the problem occurs. However if I login with a user that has no active subscription or whose Free Reg subscription has expired, DDs are zero width! The only observable difference is that in the cases where the DD works, the user is redirected straight to the edit subscriptions page whereas in the other cases, I have to select that page by going to the user profile and selecting the Subscriptions tab.
Weird, no? Please let us know if this helps your diagnosis.
Just found some more info which sounds relevant but that I cannot understand - but maybe it will help you guys to explain what is happening:
github.com/joomla/joomla-cms/issues/10001
Thanks
Jerry