edgeAADSTS50196: The server terminated an operation because it encountered a client request loop. Please contact your app vendor.

Well that does not tell you why the client is misbehaving. It can have several reasons:

on my computer it is ublock origin (adblocker) in chrome which seems to block an important part of the login communication. 

In Edge  and  ms-appstore it is the simple fact that I reinstalled yesterday Windows 10 from an 1903 usb drive and the updates had not finished .

Once they were updated to the last versions the problem went away .

This is also why it can happen on new computers as "new" does not mean "up to date" .

Most new computers have a quite big time gap between the factory installed Versions and the last up to date versions of most software.

Thank you very much!

I reset my laptop 3 times yesterday hoping that it solved 3 problems.

1. you answered
2. I am constantly asked to sign in to the fact that it is very annoying & I cannot get any work done.
3. I am having a hard time getting my previously installed basic Google apps reinstalled.

I did find another of my unused emails in "users" that I straightened out.

I am so pc illiterate that these things take me forever so I a very thankful for knowledgible people like yourself!

wer is in the doc:

"Clients that issue duplicate requests multiple times will be sent an*invalid_grant error: AADSTS50196: The server terminated an operation because it encountered a loop while processing a request**."*

https://docs.microsoft.com/en-us/azure/active-directory/develop/reference-breaking-changes#march-2019

DOES ANYONE KNOW THE ANSWER TO THIS PROBLEM?

AADSTS50196: The server terminated an operation because it encountered a client request loop. Please contact your app vendor.

THERE HAS BEEN NO REESPONSE FROM MICROSOFT      NORMAL

I did clear the browser cache using Control Panel (I like prefer) and I also ran the Disc Cleanup utility in order to clear as many unwanted files as possible. In my case, I do not think either one of those had much effect.

    I think the problem was that at some time in the past I had a M't account which had been inactive for years. When setting up a new computer I entered a phone # which differed from the one that M't "had on file." Without having access to anything M't, it was only with persistence and luck that I discovered the mismatch. With more luck, the page that showed the mismatch, also gave me the option to delete old # and reenter the correct #(tedious process  -- texted codes, e-mailed codes, and 2 password resets.)

    My deduction is that when the M't system was presented with conflicting data, it rejected both because it was unable to determine which was true and which was not true.

    I have not had any Issues with AADSTS50196 since