Hmm, I think in that case you should see failing requests with /+x where +x would be the number of failed redispatched, and it doesn’t seem to be the case here
Since the “non-working” redispatch is related to a POST request, I suspect that maybe you are hitting the same limitation as described here?
Relevant doc:
https://docs.haproxy.org/dev/configuration.html#retry-on