 <p>I had similar issues recently, also with a site hosted on Azure though I don't think that was the cause. Found out the CORS error was somehow being triggered by SQL timeout exceptions because our stored procedures were processing huge amounts of data and it was taking too long. Sped up some of the procs and most of the CORS errors stopped happening, the same needs to be done for the other procs and then they will all work again.</p> <p>Looks like you were having a different issue, but if anyone is having CORS errors that show up a few minutes after a request is made this would be worth looking into.</p>