I managed to cure it for me. I disabled auto recording suggestions and also disabled auto shut off. I don't know which of these fixed the problem, if either of them actually did, but I no longer have the problem of partially recorded films.
Welcome to our forums!
Thanks for getting in touch. I am sorry to hear you're having some problems with your TiVo box and recording. Hopefully this has been resolved since your post, if not please let us know.
All the best,