Chand's case is an interesting one. There's two types of androgen insensitivity, partial and complete. (NB no- one outside the people adjudicating on these cases and the individuals' doctors actually knows the medical details, and quite rightly so, so I will try to remember to use "it is thought".)
It is thought that Castar Semenya suffers from PAIS -she naturally produces testosterone in excess of the 10nmol/l limit and can metabolise it to build muscle. Hence the initial official ruling was that she should take androgen inhibitors. It appears that she did so for a number of years and her performance during this period, while good, was not "unbeatable".
It is thought that Duttee Chand suffers from CAIS - she produces T in excess of the limit but lacks the receptors to process it into additional muscle. For all practical purposes therefore her raised T confers no advantage. She therefore argued (at least we think this is what the argument was) that forcing her to take androgen suppressants to lower her T below an arbitrary limit (putting her at risk of side effects from the unnecessary medication) was a human rights abuse.
Her case was judged to have merit and the limit was lifted, not just for her but for all athletes whatever form of androgen insensitivity they suffered from. It is thought that this is what led to the top three places in the Rio 800m (not Chand - she's a 100m runner) being scooped by athletes widely believed to have PAIS.
Note that in and of itself this has nothing to do with trans athletes who are not intersex but genotypically and phenotypically normal members of the male sex, who happen to sincerely believe they ought to have been born female and who feel more comfortable presenting according to the stereotypes society ascribes to women. Which is a very complicated issue for them and the rest of society, but should not be conflated with the issues intersex individuals have to face.