HTTP Auth asked again and again

Hi everyone, I've read the discussion here HTTP Digest Auth & Continually Repeating Auth Prompts (on Chrome & IE, but not Safari): but I can't say the symptoms are quite similar.

We've found out that something similar to congestion may happen now and then, i.e. the resources that you've already 'authed' are loading fine but as you keep using site and navigating through it, you'll very likely get 403 status on bumch of 'new' requests and it will pop up the same prompt again for whole site.

We use traefik:v2.2 docker image (launched 4 months ago) and it seems the issue has just appeared couple of days ago. This fact makes it even more bizzare.Maybe someone has any hint to look further...

Full config for this site:

        - traefik.http.routers.demo-example-com-http.rule=Host(``)
        - traefik.http.routers.demo-example-com-http.entrypoints=http
        - traefik.http.routers.demo-example-com-http.middlewares=https-redirect
        - traefik.http.routers.demo-example-com-http.service=demo-example-com
        - traefik.http.routers.demo-example-com-https.rule=Host(``)
        - traefik.http.routers.demo-example-com-https.service=demo-example-com
        - traefik.http.routers.demo-example-com-https.entrypoints=https
        - traefik.http.routers.demo-example-com-https.tls=true
        - traefik.http.routers.demo-example-com-https.tls.certresolver=le
        - traefik.http.middlewares.demo-example-com-auth.basicauth.users=username:passwordhash
        - traefik.http.routers.demo-example-com-https.middlewares=demo-example-com-auth