Most boxes can reboot as a matter of course "periodically", but it shouldn't be this frequent by any stretch of the imagination. Boxes will also reboot if particular faults are apparent, as a self-restoring method.
All that said, rebooting (effectively) once a day is too often. If you have a TiVo as opposed to a V6, it's especially likely that the box could be trying to die. Or there could be a fault elsewhere in the TX chain and the box is dealing with that by rebooting.
In any case, report it. Either an engineer visit or box-swap is most likely needed.
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