In Firefox (tested on v78.0.2) We are starting to see warnings like the following for the first request (or after clearing cookies) to portal.
This is when the HTTP response set the cookie like...
It looks like the browser is considering the absence of the SameSite attribute to be "invalid". Whereas we were expecting it to be considered as "LAX".
This appears to be the behavior in Chrome (See LPS-107423 , and now re-tested on Chrome v84.0.4147.105 ).
The warning is concerning because it says the cookie will soon be rejected. Which presumably means the browser will not even persist it. If true, this will have huge impact on the portal.