Just adding my post to this thread. I'm having the same issue.
I will open an existing note, and get a blank screen (like I'm creating a brand new one). At that point have to wait varying amounts of time to get the actual content to appear: as little as a few seconds, to substantially more. It's annoying, as it used to be instant. It isn't my network connection or device. AFAIK, it started a few weeks ago.
My workaround was to simply un-install all updates, which left me at version 7.9.9. This (so far) seems to work well.