Getting 'Request too long' when hitting the MDI portal

[StuartH .]

Over the last week, more and more of our support teams have been seeing "Bad Request - Request Too Long.  HTTP Error 400: The size of the request headers is too long" messages when hitting https://ourATP.atp.azure.com/timeline 

Anyone else seeing this ?

Clearing cache, inprivate, different browsers, different users....none seem to fix it. Then all of a sudden it will just work.  I am assuming backend issues...but curious

[#2 · Accepted solution]

Known issue, engineering are working on a hotfix.
Once fixed, you should delete the local cookies, try again and it should work.
You can track status here:
https://health.atp.azure.com/incidents/tmcrvr4pkbbd

[#3]

Thanks for the super quick acknowledgement. Wish all MS product teams supported their products in such an open, fast and consistent way. Thanks Eli

[#4]

Another potential cause for this behavior is having a large amount of AAD group memberships resulting in a very long access token, as discovered by @Per Stromberg . So if there is no service outage and all browser caches have been cleared and the issue still persists, that is a good area to turn your attention to next.

[#5]

My workaround is to launch it using an InPrivate window.