The device may be set to auto-update applications or perhaps has had a manual update applied, as we released a new version of TPControl in December of 2015. Although usually updates do not trigger licensing revocation, factors beyond our control can change the soft-based identifier that Apple permits access to. If it changes for any reason (perhaps a prior iOS update, or restoration of the device(s) using a different devices backup), then this can trigger this effect.
More often than not, you will find that the original Token/Registration information is still on the device, but the TPC Device ID has changed - the TPC Device ID is linked to the Apple provided soft-identifier.
More details here in the related Knowledge Base article here: TPC Device ID has changed after uninstalling/reinstalling or My device says “! INVALID LICENSE” - what happened?

So, you can use the 'Token Registration' option available within Settings for TPControl (v2.5+ Android/Apple, 1.4+ Windows) to get affected devices re-registered. Only if that method fails will you need to resort to using the 'Deauthorize by Request' option available in 'TPCloud > Tokens > (token) > Deauthorize'.