Sometimes the students uninstall the profiles form their iPads. When such an iPad comes to IT support for re-installation of the profiles and we connect it to Apple Configurator then this iPad doesn't turn up in the Supervise mode of the Apple Configurator so we have to wipe it off from Prepare mode and Supervise it again. If this iPad would turn up in Supervise mode (because it went through this AC/ Mac before before) then we can save students data on it. I am trying to understand that what causes an ipad to turn up in the Supervise mode. I know that a new iPad must start from Prepare but why the Supervised ipads most of the times turn up in Prepare mode and sometimes in Supervise mode.
Which profiles are the students deleting?
I'd have to try first-hand, but I would assume that if the student deleted the MDM profile off of the iPad, Configurator would no longer see it as a Supervised device anymore.
There's also the Configurator Profile that it installs automatically to an iPad. That may be the culprit as well between Supervised and Prepare.
If this is the case though, unfortunately the only way to disallow removing the MDM profile is to do a Pre-Stage enrollment of the iPads which is a totally different distribution method from what you have.
The only way to combat this is with DEP and over the air Supervision. Because of how DEP works, it forces the iOS device to be supervised, every time. A school system that we were working with had a problem restoring iOS devices from backups because it wipes the device and causes the device to no longer be supervised. Once the devices were in DEP, it was not possible to remove the supervision profile and students could restore from iOS backups without the device becoming unsupervised.
It strikes me that you are plugging these ipads into multiple different machines. An iPad that has been supervised on one computer (and one account) will only appear as supervised on that same instance of configurator. Even with a full reset if you plug an ipad that has previously been supervised into the same instance it will automatically appear in the supervised list and will set the correct profiles again. Plugging the same ipad into a computer (or account/configurator instance) that was NOT the one that initially performed the supervision will cause it to appear in the prepare tab. I hope i read your question correctly.