CORS blocked sometimes, some redirects doesn't work

Hello, I have a really strange problem with my first deployment.
I spent the night searching for fixes and reading though netlify community posts but could’nt solve my problem, I did all the possible settings mentioned in the Topics , but still unsuccess.
This is my netlify app:
This is my heroku backend: (not sure if needed)
So my problem seems to be mainly with the JWT token based authentication. Sometimes it randomly logs me in after restart. But most of the times it just gives cors blocked error. On the other side the api that I use for my products works perfectly fine.
Also when logging out redirects are broken and it gives page not found.
Can you please do some tests and help me figure out the problem.
here is an existing account if you don’t succeed to sign up:

Hey @Krismata,

Thanks for your patience. I’ve had a check and the site doesn’t exist! How’re you getting on?