I think it's more likely hardware, I have read some comments etc online and it's actually not an uncommon issue. Oneplus official response (yeah right) is a dead battery. But in my case, I don't have to charge the phone up again before it'd turn back on, it's a simple case of plugging it in...
I'd recommend trying the cm12.1 nightlies before completely giving up on it, although it's not sounding like you're having a great time with it... Unless you're already on them?
I think it's more likely hardware, I have read some comments etc online and it's actually not an uncommon issue. Oneplus official response (yeah right) is a dead battery. But in my case, I don't have to charge the phone up again before it'd turn back on, it's a simple case of plugging it in...