This worked for me. Sign out of Icloud (Settings... “Apple Id, iCloud“). At the bottom on the right hand pane “sign out”. Delete all info? Yes.(it will all come back when you sign in)
After you are signed out of iCloud, push your home button (the big round one) and your power button at the same time. Hold both until Apple icon comes on the screen. Release buttons.
Ipad will restart shortky after. Now sign back into iCloud by reversing the sign out process.
This worked for me. It also solves some other iMessage problems.
For some reason my iPad sometimes decides to sign out of iCloud. This procedure fixes those problems for a while. It appears that iMessage on an iPad uses iCloud.