how can I keep existing messages from showing up in the iMessage sign on screen?

I am completely logged out of iMessages on my iPad. If you click on the iMessage app, the app opens, my previous messages show for a second, then the sign in box appears. It asks for my Apple ID and Password. But around the edges, you can see my previous messages. You can read some of them, but I am signed out. How can I prevent this? Im using IOS 10, but it was the same in 9

Try one or both of the following:

1. Go to Settings → General → Spotlight Search, and then disable the toggle next to "Messages".

2. Restore your device, set it up as new and do not enable iMessages.

Resetting all settings may be helpful.