Synchronization stops working on android (until mobile data switched off/on)

Hello,

Sometimes, users are reporting their devices don't get new emails in.

Devices are very different, but always android 4.0 or later.

The sync.log doesn't show any activity for those devices, and last lines don't show any error, the only solution is switch off/on mobile data, and the device starts syncing again (rebooting also works, obviously)

Anyone knows if this is an android bug or maybe a network issue?

Thanks,