The new password protect feature worked fine on the 25th April.
However I've noticed a bug on a document I was testing today 27 April.

The same document was showing a 'access denied' page though would allow me to see page past page 1.
Page 1 would not load.
The same thing happened on a newly uploaded version of that document.
The document has 16 pages with animation to the first page.
This error happened across safari and chrome browsers.
The document works fine when re-uploaded without password protection.