How to Debug an Web Forms ASP.Net 302

Question

I have an Web Forms ASP.Net App with Forms authorization, that is giving me a 302 Redirect on one page, I'd like to debug where this is happening. My thoughts are leaning towards debugging the requests using IIS? I've searched the code for this. it looks like some sort of authorization issue, but other pages in the same folder are serving just fine. I've montored the requests and got a HAR it has this:

"request": {
      "method": "GET",
      "url": "https://localhost:44300/Surveys/SurveySearchResults.aspx",
      "httpVersion": "http/2.0",
      "headers": [...]

and the response comes back:

"response": {
      "status": 302,
      "statusText": "",
      "httpVersion": "http/2.0",
      ...
           "redirectURL": "/Default.aspx",
      "headersSize": -1,
      "bodySize": -1,
      "_transferSize": 306,
      "_error": null
       ... }

What steps can I take to debug? I'm using VS2019 and IIS EXpress. All suggestions gratefully accepted, I'm stuck on this one :-)