I'm having the same problem on my iPhone ... haven't tried iPad this week. Good to know I'm not the only one; hopefully there'll be a fix available soon. I just deleted and reinstalled; fingers crossed.
The tip given here is to password protect text content in a note. If you select all of the text in a note, then you can encrypt that, which may be sufficient to your needs, but it won't encrypt attachments or images. encrypting text is helpful, but its unfortunate that it doesnt work for images or attachments. I'd like to be able to photo my credit cards and then encrypt the note ... which is why full-note encryption is so important, of course! Tx for the help.