If your iPad reboots, performs an IOS update or is taken off site it might switch to the wrong wifi source.  Please ensure the following steps are followed so that the incorrect wifi source is not connected to:

1. Settings > Wi-Fi > Ask to Join Networks >toggle to OFF (grey)

2. Click on the blue i symbol to the right of the wifi sources that you don't want the iPad connecting to (see below)

3. Select Forget this Network

4. Auto Join > toggle to OFF (grey)