My first question would be: how long ago did you power down and restart your iPad?
I met many people who answered: "a couple months ago" or "I don't remember" or "my iPad went to shutdown because the battery was low".
My advice to these people is: do it regularly, for example: once a week. And I rather tell them: "don't do restart" but do "shutdown", wait 1 min, and then start again.