BBC are now speculating that delays may be due to more junior staff individually raising concerns that while they are not going to be identified, the information in the report might make them nonetheless too easy to identify
The key word is speculating @Florianus. The BBC article says:
And there has been no attempt by civil service trade unions to delay the report or ask for retractions (Did your neighbour not let you know this, Flo?)
Only very senior civil servants will be named and those who will be named have already been informed.
But it's not impossible that more junior staff individually may have raised concerns that while they are not going to be identified, the information in the report might make them nonetheless too easy to identify
That last para is pure hokum. If that was the case the unions would be objecting on the junior civil servants' behalf and, as we know, that is not the case.. Unless none of them belong to a union, which makes them more stupid than I initially thought.