Android Update Results in "Hash of data does not match digest in descriptor" error
I realise this isn't maybe the most helpful of answers, but I thought I'd post it anyway in case someone else finds it useful.

The phone was under warranty, so took it to the local Samsung store. The support assistants commented that they'd "never seen this error before". It went in for repair and emerged fully working again.

When I asked what the problem one, I got a vague "they replaced some hardware component".

Again, not the most helpful, but enough to say that it looks like something beyond the help of a software re-install.