I have had the same issue with the Mutant HD51.
I've tried a Play TV tuner, a cheap USB tuner and a WandTv stick which uses the Afatech Af9015.
They all have the same problem, the tuners stop working after a certain period of time or after a soft reboot.
I was looking at getting the Mutant HD61 but if it has the same issue , the Zgemma H7 might be a better option due to the inbuilt DTT.