Without revisiting all the comment I've read on this (hand there's been plenty on Linkedin), I offer my personal opinion for what it's worth:
The hashing issues - the hash was supposed to ensure that HMRC could match the source of the payment to its destination. It was a nice theory but flawed for a number of reasons. The best thing would be to forget it - but that may not happen. I assume no-one will want to admit it doesn't really work, and there may be a future for it if anyone resurrects the idea of HMRC doing our deductions.
The Demands for payment - this is serious for two reasons - it shows that HMRC don't seem to be "joined-up" in the sense of wondering how an Organisation (in one example) could suddenly owe an extra £60k in tax despite having paid over everything their (respected in the Industry) software told them to. They seem to have simply picked up the phone to ask for the £60k
The second reason is that there's apparently a bit of a mess up in the way HMRC deals with people who have more than one job with the same employer - it isn't totally clear yet what this issue is, but it looks serious, given the numbers of people who do this.
Interesting times for a payroll systems geek like me.