This means the request has multiple X-Forwarded-For headers, which is wrong.
Assuming one is from cloudflare and another one is from HAProxy, there is something wrong in your HAProxy. It should have added itself to the already existing list of proxies in the existing header rather than creating one of its own.
EDIT: See Too many headers http 400 Error while using revers proxies · Issue #40421 · home-assistant/core · GitHub for a possible resolution