Response from Tech team to this issue 3-15-18
"Hi Jeff, thanks so much for your patience, my apologies for the delay. I'm on the technical support team, I'll be continuing to assist you with the issue you're experiencing with the iOS app being very slow to load note content.
I can confirm that this is a known issue on our end that our development team is actively investigate. It so far appears to be specific to setting all notebooks to offline. We are working on identifying the root cause and implementing a fix as soon as possible. It has so far been a rather complex issue to nail down, but our development team has been making good progress and they are in the process of testing a potential fix.
In the meantime, since the issue is specific to offline notebooks, one workaround would be to turn that feature off, though of course I understand this may not be ideal depending on your workflow. Another workaround that seems to help is to set the device to airplane mode, which usually speeds things up.