I am facing the same issue my frontend is in vercel and the backend is hosted on render the issue is due to google chrome's new privacy sandbox which is rolling out gradually. Now , By default chrome doesn't allow third party cookies just like in our case where backend and frontend are running on different domain.
Fixes I have figured out
Use a browser other than chrome( in my case my cookies worked fine in brave browser).
Go to chrome settings and allow third party cookies.
I am also looking for a better solution than this