Your CORS handling may not be set properly.
You can open your browser debugging tools (e.g. Chrome Developer Tools) and debug such a request. Each request should be preflighted with an OPTIONS HTTP request containing some CORS-related headers, and the response should contain all headers added through MyCorsConfiguration.
If there is no such OPTIONS request at all before the GET, it may be because you omitted the distributedTracingOrigins setting. Try to uncomment it as is and it should fix that.
If this doesn't help, please add here all details from both OPTIONS and GET requests as you see them in the browser dev tools.
I hope this helps.