There is no such thing as gender reassignment execptions.
Yes there are!
Sch. 3, part 7, para 28:
28 (1) A person does not contravene section 29, so far as relating to gender reassignment discrimination, only because of anything done in relation to a matter within sub-paragraph (2) if the conduct in question is a proportionate means of achieving a legitimate aim.
(2)The matters are—
(a)the provision of separate services for persons of each sex;
(b)the provision of separate services differently for persons of each sex;
(c)the provision of a service only to persons of one sex.
https://www.legislation.gov.uk/ukpga/2010/15/schedule/3/paragraph/28
Without this gender reassignment exception there would be no way of excluding men with a GRC from women only services.
Sch. 9, part 1, para 1 (3)(a):
(3)The references in sub-paragraph (1) to a requirement to have a protected characteristic are to be read—
(a)in the case of gender reassignment, as references to a requirement not to be a transsexual person (and section 7(3) is accordingly to be ignored);
https://www.legislation.gov.uk/ukpga/2010/15/schedule/9/part/1
Without this gender reassignment exception there would be no way of excluding men with a GRC from women only job applications.
By contrast, Sch 16, part 1 only allows associations to restrict membership to persons who share a protected characteristic. So you can have a women only organisation but because there is no gender reassignment exception there is no way to exclude those who are legally women but actually not.
The problem is that any number of organisation, employers etc., over the past decade or so have failed to take up the opportunity to argue for single sex services.
This is a big additional problem but it's a different problem for e.g. service providers than it is for e.g. membership associations because they are dealt with under different parts of the EA with different exceptions.