What makes you think it turned back? I reckon it will have fallen in the sea, but as always the MoD won't admit. Just like the 5 missing Watchkeepers.
On the key point about reliability, F35B is always going to have terrible reliability simply because of its combined hardware and software complexity. Military bods to a fair extent understand that increased mechanical complexity equals lower reliability, they've not yet realised that the same is true of software, despite all the evidence.