I don't think the police did anything wrong, nor do I see any substantive errors in the administration of justice.
I do think (more off of the back of what statisticians have said, rather than my own analysis) that there seems to have been questionable presentation of certain of the statistical evidence.
I do think that, even without considering the merits of his evidence, that Dewi Evans fell far short of his duties as an expert witness (something which he was absolutely eviscerated for by a judge in another trial).
On the merits of his evidence...it seems to be highly dubious based on what many other experts (many of which are more qualified than him) have said.
It's hard to know exactly why Letby's team did not lead their own medical evidence, which now seems as real blunder. That could have been a strategic miscalculation by her counsel, or on her own instructions for whatever reason.
I do think that her trial and appeals have been handled in a procedurally fair manner, but that there are significant evidential issues which may have produced an unfair result
To be clear, I don't think this necessarily means that she's innocent (I'm more inclined to think she is not), but I do think there are valid concerns to the extent that a re-trial might be for the best. I'll respect the CCRC's review on that issue, though.