What causes the redirect loop in AWS ELB (classic) + Keycloak?

Question

Amazon Web Services

Hello, there are 2 Keycloak servers listening on HTTPS 8443. They are closed by ELB (classic) that listens on 443 and redirects to Keycloak. I can open the main page and the login page, but after entering the data, the browser gives "too many redirects". I cleared the cache in the browser and the next couple of requests everything works, but this option is not suitable for selling. How to find the reason? Instead of ELB Classi, I also tried ALB, it does not change the essence.