Desktop to Mobile host - Loosing "Trusted devices"

Hi all

I seem to have a problem. We have a system based on tablets from China. When we setup a device, we use the TeamVeiwerHost.apk on Android, in here we put in the login credentials of our TeamVeiwer account, and a minute later we get an email where the device should be added to trusted devices. After this the device can be attached to our account

All is good. For a couple of weeks. Then we cannot reach out to the device anymore. The device is surely online, but seems to have lost it's right to be "trusted" in our teamviewer.

What is actually used for "pairing" this device as a trusted device to our account? MAC-address, or what psysically thing is used to make this deivce unique?

I am suspecting if this (what ever used) could change over time in these tablets.

Or do you have any other suggestions why it suddenly will be permanent offline, and the only thing making it coming back is to reapprove as trusted device?

It's kind of a big problem as most of the devices is far away and we cannot access them again.

Thank for you support.