On iPad, the Check in button on Walk-up is disabled after some time and the user needs to refresh the page manually to enable the button again.
There can be different causes for the issue, one of the most common ones is that the system property glide.ui.session_timeout is not set in the instance.
Walk-up is designed to auto-refresh with the help of Walk-up keepalive. Walk-up keepalive takes the value of glide.ui.session_timeout and sets it to auto-refresh at an interval half of the timeout value. If this value is set to 1 minute, it will refresh every 30 seconds. This way it keeps the session alive.
Make sure the system property glide.ui.session_timeout contains a value.