Going back to the original report, I would be very interested to know how quickly the RCD trips when you press the test button.
The readings on the report say >500 (x1) and >410 (x5). Assuming these are milliseconds, I think that even without a testing machine you could discern if it trips in 'about half a second' or 'instantaneously'.
If it proves that the RCD is in fact ok, then as far as I can see we are now reduced to one incorrect breaker and a possible shower circuit issue.
General point -
When I (rarely) do remedial work for someone else's EICR, if I disagree with a C2 I justify why on my write up citing relevant regulations and photographic evidence why . You don't actually need a certificate that says "satisfactory", you need written proof that required remedial work has happened, and for me I just use a letter. Here's two excepts from a recent one I wrote:
View attachment 93954
and a bit later:
View attachment 93955
My point is that you don't need the same person to do remedials, and you don't need another EICR, you just need someone to evaluate matters and do required remedials who takes a professional approach.
All the best with this.