POST from Firefox is sent twice to Tomcat backend

I have Traefik Proxy 2.7.0 with a single server service running tomcat with oracle ords for apex access,
I can login fine from Chrome, but when I login with Firefox I see the request is sent twice and causing my session to become invalid straight away.
It's a (single) POST request and the FF network tab shows a single request, and when I bypass Traefik and go through Apache HTTPD Reverse Proxy it works fine also.
Both traefik debug logs and http capture (between Traefik & Tomcat) show 2 POST requests.
I am not sure how I would capture traffic from browser to Traefik as only https can be used,
but I am wondering if anyone has ideas and/or seen this before?

Edit: I did a wireshare with TLS decryption and saw 1 request going to Traefik
This screenshot shows a ForwardURL in the 2nd POST? (just checked again, but it's at the end of the line of line#2 for post1 )

and this is a trace from the responses from the backend, left is after a POST from Chrome, right is from FF, which results in the 2nd POST


      rule = "PathPrefix(`/apex`)"
      service = "tomcat"
        url = ""