Update 17.4.1 iMessage stopped working iPad
Both iMessage and FaceTime signed me out and I’m unable to sign back in. This happened after this update. I can’t even get into iMessage to turn it on or off.
iPad 2, iOS 9
Do you use VPN? If so, delete the VPN profile in Settings/General/VPN & Device Management/VPN. Don't just turn it off; delete the profile.